exif_transpose overwrites the original image exif

[artemisart]

What did you do?

Use ImageOps.exif_tranpose on an image with an EXIF orientation code (not in [None, 0, 1]).

What did you expect to happen?

exif_transpose() should be immutable and returns a new image with the correct orientation.

What actually happened?

exif_transpose() returns a new image but also modifies the original image exif info in-place (deletes the orientation, key 0x112).
It's a pretty big problem if your work with rotated images because it breaks the original images, if you e.g. call again exif_transpose() on it the EXIF orientation value is not there but the image content is not correctly rotated.

What are your OS, Python and Pillow versions?

• OS: ubuntu 18.04
• Python: 3.8.8
• Pillow: 8.2.0

Code

import PIL, PIL.ImageOps
# if you have an image with exif
pil = PIL.Image.open(file)
# otherwise
import requests
resp = requests.get('https://raw.githubusercontent.com/recurser/exif-orientation-examples/master/Portrait_3.jpg', stream=True)
resp.raw.decode_content = True
pil = PIL.Image.open(resp.raw)

print(pil.getexif().get(0x0112))  # 3
correct_image = PIL.ImageOps.exif_transpose(pil)
print(pil.getexif().get(0x0112))  # None, but should be 3

Proposed fix

Replace the first line of exif_tranpose in https://pillow.readthedocs.io/en/stable/_modules/PIL/ImageOps.html#exif_transpose with

from copy import deepcopy  # copy may be enough, I didn't try it

-    exif = image.getexif()
+    exif = deepcopy(image.getexif())

[radarhere]

Yep, good point. I've created PR #5547 to resolve this - my method was not to copy the Image.Exif instance of the original image, but to create a new instance from the output image.