During the fall this was a recurring problem for me as well, especially the pilfering of my supersized scans for out-of-print DVDs. To demonstrate both the condition and authenticity of my own offerings, I always take the time to scan them front, back, and top seal. For lazier sellers, this was something just too tempting I guess...
For the most part, those ripping-off my images responded reasonably well to a strong warning...typically, something along the lines of "Hey, that image is not stock or clip art--it's my scan of my item. Just because yours looks similar, you have no right to use mine and call it your own." But basically, I just got tired having to go through that Ask Seller A Question routine every other week.
For what it may be worth, here are my best solutions:
Develop a personal style of photography, scanning, and listing layout. Even if someone tries to rip you, savvy buyers will recognize your distinctive image/listing style...in fact, many eBayers will even flag you about such suspect activity. It's a kind of 'branding' which also works for you in terms of 'bidder recognition'.
Most of those ripping your images/text do so because they're just plain lazy...make your listings hard to block copy through use of tables, columns and other HTML layout tricks. For example, I've added an auto-sizing column to my listings which not only serves the info-flow pretty well, but also is one beggar to copy effectively. Develop an HTML template that's relatively easy for you to use, but difficult for others to make work without time consuming tinkering and tweaking. Again, we're talking mainly about laziness here as the motive for ripping. Kill 'em with complexity.
Add an overlay signature to your scans. Lots of ways to achieve this, and some folks have pretty much automated the process through macros in their photo-editing software. For me, it's a manual but simple process: just a scanned sig with a solid gray background that I quickly plop in through copy/paste, make transparent by sliding off the background channel under my layer options, then flatten, resize and position. Choose a strategic spot where it will be all but impossible for the ripper to remove, but still reasonably unobtrusive to the viewer. Be creative--again, there is an opportunity to promote your own image while thwarting the rippers.
Don't bother doing anything to scans that are going to be uploaded to eBay at the standard image/size listing resolution--no one will bother with those, and even if the do, the results when they do list will look so crappy, it won't help them anyway.
And finally, take heart...I think most frequent users of the system do recognize these rips when they see them, especially if they're familiar with a particular type of item or genre. They may not remember exactly where or when they saw an image before (although your regulars quite often will), but they will probably go "Ah-a...that image was taken from another listing!" or "That's another writer's style!"
Finally, if you are using image hosting and finding other listings linked to yours, try a rude "bait and switch". After their listing is already active, and especially after it has bids on it, simply rename your original image and substitute something nasty instead...ideally just scatological or salacious enough to get their auction pulled.
Of course, no guarantees with any of this, but since I've implemented some of these practices, my image/listing rips have become almost non-existent.
