diff --git a/src/pretix/api/views/upload.py b/src/pretix/api/views/upload.py
index 767d427bbb..bd75a7d982 100644
--- a/src/pretix/api/views/upload.py
+++ b/src/pretix/api/views/upload.py
@@ -21,6 +21,7 @@
 #
 import datetime
 
+from django.core.exceptions import ValidationError as DjangoValidationError
 from django.utils.timezone import now
 from oauth2_provider.contrib.rest_framework import OAuth2Authentication
 from rest_framework.authentication import SessionAuthentication
@@ -33,6 +34,9 @@ from pretix.api.auth.device import DeviceTokenAuthentication
 from pretix.api.auth.permission import AnyAuthenticatedClientPermission
 from pretix.api.auth.token import TeamTokenAuthentication
 from pretix.base.models import CachedFile
+from pretix.helpers.images import (
+    IMAGE_TYPES, validate_uploaded_file_for_valid_image,
+)
 
 ALLOWED_TYPES = {
     'image/gif': {'.gif'},
@@ -61,6 +65,13 @@ class UploadView(APIView):
                 name=file_obj.name,
                 type=content_type
             ))
+
+        if content_type in IMAGE_TYPES:
+            try:
+                validate_uploaded_file_for_valid_image(file_obj)
+            except DjangoValidationError as e:
+                raise ValidationError(e.message)
+
         cf = CachedFile.objects.create(
             expires=now() + datetime.timedelta(days=1),
             date=now(),
diff --git a/src/pretix/base/forms/questions.py b/src/pretix/base/forms/questions.py
index 9fcc7342e7..e6419fe758 100644
--- a/src/pretix/base/forms/questions.py
+++ b/src/pretix/base/forms/questions.py
@@ -531,7 +531,7 @@ class PortraitImageField(SizeValidationMixin, ExtValidationMixin, forms.FileFiel
                     code='aspect_ratio_not_3_by_4',
                 )
         except Exception as exc:
-            logger.exception('foo')
+            logger.exception('Could not parse image')
             # Pillow doesn't recognize it as an image.
             if isinstance(exc, ValidationError):
                 raise
diff --git a/src/pretix/base/models/items.py b/src/pretix/base/models/items.py
index fed9e29f7f..f90b9eec02 100644
--- a/src/pretix/base/models/items.py
+++ b/src/pretix/base/models/items.py
@@ -62,6 +62,7 @@ from pretix.base.models.base import LoggedModel
 from pretix.base.models.fields import MultiStringField
 from pretix.base.models.tax import TaxedPrice
 
+from ...helpers.images import ImageSizeValidator
 from .event import Event, SubEvent
 
 
@@ -429,7 +430,8 @@ class Item(LoggedModel):
     picture = models.ImageField(
         verbose_name=_("Product picture"),
         null=True, blank=True, max_length=255,
-        upload_to=itempicture_upload_to
+        upload_to=itempicture_upload_to,
+        validators=[ImageSizeValidator()]
     )
     available_from = models.DateTimeField(
         verbose_name=_("Available from"),
diff --git a/src/pretix/control/forms/__init__.py b/src/pretix/control/forms/__init__.py
index c1196c3d8a..091c087cd5 100644
--- a/src/pretix/control/forms/__init__.py
+++ b/src/pretix/control/forms/__init__.py
@@ -51,6 +51,9 @@ from django_scopes.forms import SafeModelMultipleChoiceField
 from pretix.helpers.hierarkey import clean_filename
 
 from ...base.forms import I18nModelForm
+from ...helpers.images import (
+    IMAGE_EXTS, validate_uploaded_file_for_valid_image,
+)
 
 # Import for backwards compatibility with okd import paths
 from ...base.forms.widgets import (  # noqa
@@ -220,6 +223,10 @@ class ExtValidationMixin:
             ext = ext.lower()
             if ext not in self.ext_whitelist:
                 raise forms.ValidationError(_("Filetype not allowed!"))
+
+            if ext in IMAGE_EXTS:
+                validate_uploaded_file_for_valid_image(data)
+
         return data
 
 
diff --git a/src/pretix/helpers/images.py b/src/pretix/helpers/images.py
new file mode 100644
index 0000000000..c347bb9f9d
--- /dev/null
+++ b/src/pretix/helpers/images.py
@@ -0,0 +1,85 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+import logging
+from io import BytesIO
+
+from django.core.exceptions import ValidationError
+from django.utils.translation import gettext_lazy as _
+from PIL.Image import MAX_IMAGE_PIXELS, DecompressionBombError
+
+IMAGE_TYPES = {'image/gif', 'image/jpeg', 'image/png'}
+IMAGE_EXTS = {'.gif', '.jpg', '.jpeg', '.png'}
+
+
+logger = logging.getLogger(__name__)
+
+
+def validate_uploaded_file_for_valid_image(f):
+    if f is None:
+        return None
+
+    from PIL import Image
+
+    # We need to get a file object for Pillow. We might have a path or we might
+    # have to read the data into memory.
+    if hasattr(f, 'temporary_file_path'):
+        file = f.temporary_file_path()
+    else:
+        if hasattr(f, 'read'):
+            file = BytesIO(f.read())
+        else:
+            file = BytesIO(f['content'])
+
+    try:
+        try:
+            image = Image.open(file)
+            # verify() must be called immediately after the constructor.
+            image.verify()
+        except DecompressionBombError:
+            raise ValidationError(_(
+                "The file you uploaded has a very large number of pixels, please upload a picture with smaller dimensions."
+            ))
+
+        # load() is a potential DoS vector (see Django bug #18520), so we verify the size first
+        if image.width * image.height > MAX_IMAGE_PIXELS:
+            raise ValidationError(_(
+                "The file you uploaded has a very large number of pixels, please upload a picture with smaller dimensions."
+            ))
+    except Exception as exc:
+        logger.exception('Could not parse image')
+        # Pillow doesn't recognize it as an image.
+        if isinstance(exc, ValidationError):
+            raise
+        raise ValidationError(_(
+            "Upload a valid image. The file you uploaded was either not an image or a corrupted image."
+        )) from exc
+    if hasattr(f, 'seek') and callable(f.seek):
+        f.seek(0)
+
+
+class ImageSizeValidator:
+    def __call__(self, image):
+        if image.width * image.height > MAX_IMAGE_PIXELS:
+            raise ValidationError(_(
+                "The file you uploaded has a very large number of pixels, please upload a picture with smaller dimensions."
+            ))
+        return image
diff --git a/src/pretix/testutils/api.py b/src/pretix/testutils/api.py
index 2d5d1ce3a8..a0e19255bc 100644
--- a/src/pretix/testutils/api.py
+++ b/src/pretix/testutils/api.py
@@ -29,4 +29,4 @@ class UploadRenderer(BaseRenderer):
 
     def render(self, data, accepted_media_type=None, renderer_context=None):
         self.media_type = data['media_type']
-        return data['file']
+        return data['file'].read()
diff --git a/src/tests/api/test_cart.py b/src/tests/api/test_cart.py
index 21af7788bd..8849d64484 100644
--- a/src/tests/api/test_cart.py
+++ b/src/tests/api/test_cart.py
@@ -29,6 +29,7 @@ from django.core.files.base import ContentFile
 from django.utils.timezone import now
 from django_scopes import scopes_disabled
 from pytz import UTC
+from tests.const import SAMPLE_PNG
 
 from pretix.base.models import Question, SeatingPlan
 from pretix.base.models.orders import CartPosition
@@ -467,7 +468,7 @@ def test_cartpos_create_answer_validation(token_client, organizer, event, item,
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
diff --git a/src/tests/api/test_checkin.py b/src/tests/api/test_checkin.py
index 9132e9af89..6d76e13a80 100644
--- a/src/tests/api/test_checkin.py
+++ b/src/tests/api/test_checkin.py
@@ -32,6 +32,7 @@ from django_countries.fields import Country
 from django_scopes import scopes_disabled
 from i18nfield.strings import LazyI18nString
 from pytz import UTC
+from tests.const import SAMPLE_PNG
 
 from pretix.api.serializers.item import QuestionSerializer
 from pretix.base.models import (
@@ -1057,7 +1058,7 @@ def test_question_upload(token_client, organizer, clist, event, order, question)
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
diff --git a/src/tests/api/test_checkinrpc.py b/src/tests/api/test_checkinrpc.py
index ce908d32cf..8a9e93efe7 100644
--- a/src/tests/api/test_checkinrpc.py
+++ b/src/tests/api/test_checkinrpc.py
@@ -30,6 +30,7 @@ from django_countries.fields import Country
 from django_scopes import scopes_disabled
 from i18nfield.strings import LazyI18nString
 from pytz import UTC
+from tests.const import SAMPLE_PNG
 
 from pretix.api.serializers.item import QuestionSerializer
 from pretix.base.models import Checkin, InvoiceAddress, Order, OrderPosition
@@ -563,7 +564,7 @@ def test_question_upload(token_client, organizer, clist, event, order, question)
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
diff --git a/src/tests/api/test_events.py b/src/tests/api/test_events.py
index a043cde612..6745d4423d 100644
--- a/src/tests/api/test_events.py
+++ b/src/tests/api/test_events.py
@@ -44,6 +44,7 @@ from django.utils.timezone import now
 from django_countries.fields import Country
 from django_scopes import scopes_disabled
 from pytz import UTC
+from tests.const import SAMPLE_PNG
 
 from pretix.base.models import (
     Event, InvoiceAddress, Order, OrderPosition, Organizer, SeatingPlan,
@@ -1351,7 +1352,7 @@ def test_patch_event_settings_file(token_client, organizer, event):
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
@@ -1363,7 +1364,7 @@ def test_patch_event_settings_file(token_client, organizer, event):
         '/api/v1/upload',
         data={
             'media_type': 'application/pdf',
-            'file': ContentFile('file.pdf', 'invalid pdf content')
+            'file': ContentFile('invalid pdf content')
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.pdf"',
diff --git a/src/tests/api/test_items.py b/src/tests/api/test_items.py
index d3def769d4..7f96d9365e 100644
--- a/src/tests/api/test_items.py
+++ b/src/tests/api/test_items.py
@@ -43,6 +43,7 @@ from django.core.files.base import ContentFile
 from django_countries.fields import Country
 from django_scopes import scopes_disabled
 from pytz import UTC
+from tests.const import SAMPLE_PNG
 
 from pretix.base.channels import get_all_sales_channels
 from pretix.base.models import (
@@ -1119,7 +1120,7 @@ def test_item_file_upload(token_client, organizer, event, item):
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
@@ -1143,7 +1144,7 @@ def test_item_file_upload(token_client, organizer, event, item):
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
diff --git a/src/tests/api/test_order_change.py b/src/tests/api/test_order_change.py
index 7b4877f1b5..da78eba7a7 100644
--- a/src/tests/api/test_order_change.py
+++ b/src/tests/api/test_order_change.py
@@ -31,6 +31,7 @@ from django.utils.timezone import now
 from django_countries.fields import Country
 from django_scopes import scopes_disabled
 from pytz import UTC
+from tests.const import SAMPLE_PNG
 
 from pretix.base.models import (
     InvoiceAddress, Order, OrderPosition, Question, SeatingPlan,
@@ -1018,7 +1019,7 @@ def test_position_update_question_handling(token_client, organizer, event, order
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
diff --git a/src/tests/api/test_order_create.py b/src/tests/api/test_order_create.py
index eedc77b615..4cc1273179 100644
--- a/src/tests/api/test_order_create.py
+++ b/src/tests/api/test_order_create.py
@@ -32,6 +32,7 @@ from django.utils.timezone import now
 from django_countries.fields import Country
 from django_scopes import scopes_disabled
 from pytz import UTC
+from tests.const import SAMPLE_PNG
 
 from pretix.base.models import (
     InvoiceAddress, Order, OrderPosition, Question, SeatingPlan,
@@ -1424,7 +1425,7 @@ def test_order_create_answer_validation(token_client, organizer, event, item, qu
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
diff --git a/src/tests/api/test_organizers.py b/src/tests/api/test_organizers.py
index 576d486361..bb1123931d 100644
--- a/src/tests/api/test_organizers.py
+++ b/src/tests/api/test_organizers.py
@@ -21,6 +21,7 @@
 #
 import pytest
 from django.core.files.base import ContentFile
+from tests.const import SAMPLE_PNG
 
 from pretix.testutils.mock import mocker_context
 
@@ -130,7 +131,7 @@ def test_patch_organizer_settings_file(token_client, organizer):
         '/api/v1/upload',
         data={
             'media_type': 'image/png',
-            'file': ContentFile('file.png', 'invalid png content')
+            'file': ContentFile(SAMPLE_PNG)
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
@@ -142,7 +143,7 @@ def test_patch_organizer_settings_file(token_client, organizer):
         '/api/v1/upload',
         data={
             'media_type': 'application/pdf',
-            'file': ContentFile('file.pdf', 'invalid pdf content')
+            'file': ContentFile('invalid pdf content')
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.pdf"',
diff --git a/src/tests/api/test_upload.py b/src/tests/api/test_upload.py
index c9b8b765d3..955130f378 100644
--- a/src/tests/api/test_upload.py
+++ b/src/tests/api/test_upload.py
@@ -19,8 +19,14 @@
 # You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
 # <https://www.gnu.org/licenses/>.
 #
+import io
+import math
+
 import pytest
 from django.core.files.base import ContentFile
+from PIL import Image
+from PIL.Image import MAX_IMAGE_PIXELS
+from tests.const import SAMPLE_PNG
 
 
 @pytest.mark.django_db
@@ -29,7 +35,7 @@ def test_upload_file(token_client):
         '/api/v1/upload',
         data={
             'media_type': 'application/pdf',
-            'file': ContentFile('file.pdf', 'invalid pdf content')
+            'file': ContentFile('invalid pdf content')
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.pdf"',
@@ -44,9 +50,74 @@ def test_upload_file_extension_mismatch(token_client):
         '/api/v1/upload',
         data={
             'media_type': 'application/pdf',
-            'file': ContentFile('file.png', 'invalid pdf content')
+            'file': ContentFile('invalid pdf content')
         },
         format='upload',
         HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
     )
     assert r.status_code == 400
+    assert r.data == ['File name "file.png" has an invalid extension for type "application/pdf"']
+
+
+@pytest.mark.django_db
+def test_upload_file_extension_not_allowed(token_client):
+    r = token_client.post(
+        '/api/v1/upload',
+        data={
+            'media_type': 'application/octet-stream',
+            'file': ContentFile('invalid pdf content')
+        },
+        format='upload',
+        HTTP_CONTENT_DISPOSITION='attachment; filename="file.bin"',
+    )
+    assert r.status_code == 400
+    assert r.data == ['Content type "application/octet-stream" is not allowed']
+
+
+@pytest.mark.django_db
+def test_upload_invalid_image(token_client):
+    r = token_client.post(
+        '/api/v1/upload',
+        data={
+            'media_type': 'image/png',
+            'file': ContentFile('invalid png content')
+        },
+        format='upload',
+        HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
+    )
+    assert r.status_code == 400
+    assert r.data == ['Upload a valid image. The file you uploaded was either not an image or a corrupted image.']
+
+
+@pytest.mark.django_db
+def test_upload_valid_image(token_client):
+    r = token_client.post(
+        '/api/v1/upload',
+        data={
+            'media_type': 'image/png',
+            'file': ContentFile(SAMPLE_PNG)
+        },
+        format='upload',
+        HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
+    )
+    assert r.status_code == 201
+
+
+@pytest.mark.django_db
+@pytest.mark.filterwarnings("ignore")
+def test_upload_image_with_invalid_dimensions(token_client):
+    d = int(math.sqrt(MAX_IMAGE_PIXELS)) + 100
+    img = Image.new('RGB', (d, d), color='red')
+    output = io.BytesIO()
+    img.save(output, format='PNG')
+    r = token_client.post(
+        '/api/v1/upload',
+        data={
+            'media_type': 'image/png',
+            'file': ContentFile(output.getvalue())
+        },
+        format='upload',
+        HTTP_CONTENT_DISPOSITION='attachment; filename="file.png"',
+    )
+    assert r.status_code == 400
+    assert r.data == ['The file you uploaded has a very large number of pixels, please upload a picture with smaller dimensions.']
diff --git a/src/tests/const.py b/src/tests/const.py
new file mode 100644
index 0000000000..b744653fed
--- /dev/null
+++ b/src/tests/const.py
@@ -0,0 +1,26 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+
+# This is a very short, but valid PNG
+SAMPLE_PNG = b'\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x01\x00\x00\x00\x01\x00\x01\x03\x00\x00\x00f\xbc:%\x00\x00' \
+             b'\x00\x03PLTE\xb5\xd0\xd0c\x04\x16\xea\x00\x00\x00\x1fIDATh\x81\xed\xc1\x01\r\x00\x00\x00\xc2\xa0\xf7Om' \
+             b'\x0e7\xa0\x00\x00\x00\x00\x00\x00\x00\x00\xbe\r!\x00\x00\x01\x9a`\xe1\xd5\x00\x00\x00\x00IEND\xaeB`\x82'