I use a software program called "Thumber" to organize and process my image files. This software is available at a very reasonable price (currently $18 USD) from the author, Max Lyons, at .
Thumber can add comments to any JPEG file.
There is also a FREE Windows based program by Eric Magnusom called "Edjpgcom" that can read and edit the comment blocks, downloadable at .
These comments are inserted into the image file in such a way that they have no effect on how the image is displayed. However, Thumber (and any other software that can decode comment blocks) can read back and display the comments. A comment is limited to 32K in size, and can contain any textual information. Comments that Thumber inserts into an image are unrelated and separate from any EXIF or APP12 data that the image may contain.
Adding a comment to an image file is a good way of storing information permanently inside an image. Unlike software that catalogs images using a database scheme, the comment can never become "unattached" from the image when it is inserted by Thumber. If you edit the image using other software, however, it may not retain the comment.
Because comments are stored as text inside the image file, you can use Windows' "Find Files and Folders" feature to search for images that contain particular comments. From Windows Explorer choose the "Tools" menu item, then "Find", and then "Files or Folders". Search for comments by entering the search term in the "Containing Text" entry box under the advanced tab.