Python PIL image Verify returns None

Question

I am developing a tool which retrieves a JPG from an API and processes it. The source of the image cannot be trusted and I want to test if the image is a valid JPG (which is the only image type allowed).

I encountered an error with PIL that I am unable to fix. Below is my code:

image = StringIO(base64.b64decode(download['file']))
img = Image.open(image)
if img.verify():
    print 'Valid image'
else:
    print 'Invalid image'

However, it seems that img.verify() returns None. I can call other functions on the open image like img.size() which returns the size. I get the following output when I try to debug the code:

img = Image.open(image)
print img
print img.size()
print img.verify()

[2018-01-09 20:56:43,715: WARNING/Worker-1] <PIL.JpegImagePlugin.JpegImageFile image mode=RGB size=2577x1715 at 0x7F16E17DC9D0>
[2018-01-09 20:56:43,716: WARNING/Worker-1] (2577, 1715)
[2018-01-09 20:56:43,716: WARNING/Worker-1] None

Has someone encountered the same issue?

Answer 1

According to the docs, Image#verify (or the PIL docs for verify) raises an exception if there is a problem with the image and does nothing otherwise.

To use #verify, you probably want something like this:

image = StringIO(base64.b64decode(download['file']))
img = Image.open(image)
try:
    img.verify()
    print('Valid image')
except Exception:
    print('Invalid image')

Additionally, you might want to also check that the image is actually a JPG by looking at the image format:

if img.format == 'JPEG':
     print('JPEG image')
else:
     print('Invalid image type')