Today I stumbled upon JPEGSnoop, "a free Windows application that examines and decodes the inner details of JPEG and MotionJPEG AVI files. It can also be used to analyze the source of an image to test its authenticity." (quote)

While not being free in the FOSS sense, its photo integrity checks deserve special mention:
- It can verify whether a photo was modified in an image editor or comes directly from the camera
- It can suggest a list of possible camera models even for metadata-wiped photos (Note: if the image was modified in an editor, it will provide the editors name and a possible jpeg quality setting)

JPEGSnoop determines this information by comparing JPEG Quantisation Table Checksums, which is much more manipulation-safe than just relying on EXIF/IPTC Metadata.

It would be nice to see similar metadata validation capabilities in Exiftool (e.g. to validate that an image was unmodified, that the metadata hasn't been tampered,..), but I'm afraid that's a bit off the road and might also exceed Perl's data processing capabilities. But maybe this can be achieved by embedding external tools?