Basicaly some way to spesify an id and class value for an image *from the image description page*
Not sure what kind of syntax would be best for this, "traditional" magic words don't take parameters so something like __META id ="ifd" class="ifd"__ might seem "ugly" or strange, on the other hand a more function-ish appraoch like {{#meta: id="ifd"|class="ifd"}} would not be expected to have the effect I'm suggesting. Ideas on this would be most welcome ("meta" is probably not the best name either).
Anyway the general idea is this: By whatever means is deemed the best syntax it should be possible to spesify an arbitrary id and class value (except one that colide with existing "hard coded" values, maybe prefix all user spesified values in some way to avoid problems) for an image from it's description page. The "thumbnailing code" would then apply this to either the div or img tag of the image (depending on wether or not it's framed). The admins on any given Wiki are then free to add JavaScript functions and CSS classes to interact with the image in just about any way they can imagine.
For Wikipedia projects a few obvious uses are: "Highlighting" images that are marked for deletion, or as missing source info and so on in various ways. This may be as simple as adding a red border around the image, or making use of a JavaScript to superimpose a warning on top of the image or adding something to the image caption, add a explanatory tooltip or any number of other possibilities that are best left to each project to descide.
Replacing the visible thumbnail with a warning sign if a fair use image is used in User: space.
Optional (add some code to your user CSS/JS page) ability to have fair use, featured and various other kinds of images marked in special ways.
With a bit of effort it might even be used in combination with a template like {{fair use in}} to have a warning appear on the image if it's used in any other page than the one(s) mentioned in the tag (take the page name as the class parameter and have a JavaScript check against it).
I'm sure there are lots of other creative uses I can't think of right now.
I guess this would reqire a new row in the image table to store these values.
If at all possible this should work across wikis too, so an image marked for deletion on Commons would expose it's "deletion" class to all projects that use the image too (leaving it up to them how to "mark" the image localy).
Any reason something like this would *not* be possible (or desierable). There might be problems I haven't though about, but I think it would be a quite usefull feature. If allowing users to set arbitrary values are too "hard" a handfull of hard coded magic words (like __DELETION__ or whatever) would still be better than nothing, but the more flexible the better I would say. Accessability should not be a problem, if someone doesn't have JavaScript or CSS eneabled the worst that can happen is that everyting looks just like it does today with no extra "markings" on any images. Projects just have to be carefull not to use this layout purposes, just like they already have to be carefull not to rely on fancy CSS to make articles "work" properly.
If this is not totaly shot down I'm planning to submit a feature request via bugzilla, just wanted to get a bit of input from you guys first (like what would be the best syntax, any additional fetures that would be usefull related to this etc).