diff --git a/wagtail/wagtailimages/models.py b/wagtail/wagtailimages/models.py
index f0be0fe4dd..24fd1f0bf1 100644
--- a/wagtail/wagtailimages/models.py
+++ b/wagtail/wagtailimages/models.py
@@ -4,7 +4,7 @@ import os.path
 from taggit.managers import TaggableManager
 
 from django.core.files import File
-from django.core.exceptions import ImproperlyConfigured, ObjectDoesNotExist, ValidationError
+from django.core.exceptions import ImproperlyConfigured, ObjectDoesNotExist
 from django.db import models
 from django.db.models.signals import pre_delete
 from django.dispatch.dispatcher import receiver
@@ -17,6 +17,8 @@ from unidecode import unidecode
 
 from wagtail.wagtailadmin.taggable import TagSearchable
 from wagtail.wagtailimages.backends import get_image_backend
+from .utils import validate_image_format
+
 
 class AbstractImage(models.Model, TagSearchable):
     title = models.CharField(max_length=255, verbose_name=_('Title') )
@@ -34,12 +36,7 @@ class AbstractImage(models.Model, TagSearchable):
             filename = prefix[:-1] + dot + extension
         return os.path.join(folder_name, filename)
 
-    def file_extension_validator(ffile):
-        extension = ffile.name.split(".")[-1].lower()
-        if extension not in ["gif", "jpg", "jpeg", "png"]:
-            raise ValidationError(_("Not a valid image format. Please use a gif, jpeg or png file instead."))
-
-    file = models.ImageField(verbose_name=_('File'), upload_to=get_upload_to, width_field='width', height_field='height', validators=[file_extension_validator])
+    file = models.ImageField(verbose_name=_('File'), upload_to=get_upload_to, width_field='width', height_field='height', validators=[validate_image_format])
     width = models.IntegerField(editable=False)
     height = models.IntegerField(editable=False)
     created_at = models.DateTimeField(auto_now_add=True)
diff --git a/wagtail/wagtailimages/utils.py b/wagtail/wagtailimages/utils.py
new file mode 100644
index 0000000000..627a8f1215
--- /dev/null
+++ b/wagtail/wagtailimages/utils.py
@@ -0,0 +1,27 @@
+import os
+
+from PIL import Image
+
+from django.core.exceptions import ValidationError
+from django.utils.translation import ugettext_lazy  as _
+
+
+def validate_image_format(f):
+    # Check file extension
+    extension = os.path.splitext(f.name)[1].lower()[1:]
+
+    if extension == 'jpg':
+        extension = 'jpeg'
+
+    if extension not in ['gif', 'jpeg', 'png']:
+        raise ValidationError(_("Not a valid image. Please use a gif, jpeg or png file with the correct file extension."))
+
+    # Open image file
+    file_position = f.tell()
+    f.seek(0)
+    image = Image.open(f)
+    f.seek(file_position)
+
+    # Check that the internal format matches the extension
+    if image.format.upper() != extension.upper():
+        raise ValidationError(_("Not a valid %s image. Please use a gif, jpeg or png file with the correct file extension.") % (extension.upper()))