|Exif TIFF Tag UserComment|
TIFF Tag Reference
TIFF Tag UserComment
Keywords or comments on the image; complements ImageDescription.
This tag is without the character code limitations of the ImageDescription tag.
The character code used in the UserComment tag is identified based on an ID code in a fixed 8-byte area at the start of the tag data area. The unused portion of the area is padded with NULL ("00.H").
The specification defines these possible values for the first 8 bytes of the tag data:
ASCII (hex 41, 53, 43, 49, 49, 00, 00, 00): ITU-T T.50 IA5
The value of Count N is determined based on the 8 bytes in the character code area and the number of bytes in the user comment part. Since the TYPE is not ASCII, NULL termination is not necessary.