Django - Upload a valid image
And don't forget about jpeg-lib! Without it PIL willn't understand with what format it can works.
I'm using Ubuntu, Django 1.3, Python 2.7.
When I try to upload certain types of image, I get this message:

Upload a valid image. The file you uploaded was either not an image or a corrupted image.

It's happening with PNG and JPG (the formats that I need).
tiff and gif (that I don't and will never care about) are working.
What can I do ?