Image Metadata (Exif)
Some image file formats, such as JPG, store various metadata about their contents. This can be information such as where a photo was taken or which camera model was used. This can be useful information for puzzle solving, especially for geocaching or puzzles that involve coordinates.
See also: Code-Breaking overview | Low contrast images | Music steganography | Openpuff | Outguess | Spectrograms | Steghide | Stereograms