I’m no expert, but EXIF specs have a tag labeled 0x9286 UserComment that might be possible to use. However, I don’t think it supports modern character sets so it’s probably too limiting to work with. Someone more knowledgeable can chime in. https://exiftool.org/TagNames/EXIF.html
Discussion
There are also different places/ways it is stored from one image type to another.. probably easier and more accurate to make a database.