In his latest post on the SitePoint PHP blog today, Harry Fuecks talks about a problem he was having - adding comments to pictures to be stored with them, not seperately. He's found a solution and it involves g-scripts.
One particular problem is adding comments to images; most archiving software (like gthumb) has you store stuff seperately from the images, maintaining their own databases (in the case of gthumb, under ~/.gnome2/gthumb). But I'd rather have comments stay with the image (e.g. using Exif - there are other ways but Exif wins on being widely supported).
He talks about the use of the g-scripts and something called Zenity to make the popup inputs for the comments. After some quick tips to be sure everything's set up, he demonstrates how to, with PHP scripts and Zenity, to integrate the comments into the Exif data of your files.