Embedding For Search?

Does anybody know of a way of "tagging" an images either in the file naming convention or in the metadata so that google images can find them? I've had all kinds of people swiping my images from Flickr and my personal site. I try to keep them low rez, but I'm reluctant to watermark, just a pet peeve of mine.

digimarc makes a plug in for photoshop to track images, and i've heard watermarker.com does the same.

do a watermark anyway for the copyright office. they want a clear line if the image is copyrighted.

the digimarc plugin is quite expensive i believe.

I'd just go for a normal watermark as i'm sure there must be a hack for the digimarc thing floating around somewhere.