Some of you may already be aware of this, but I just read about this in Consumer Reports, about a web site selling an herbal supplement with impressive "before and after" photos:
"Who's behind weight-loss testimonials? A reader with inside info about this one reveals that "Georges" from Paris isn't who he seems. "That's my son Sam," the reader writes. "We live in Springfield, Ill." The pictures came from a body-building site to which Sam belongs, his dad says. And the results didn't come from the touted herbal product. "Sam spent three years and countless hours at the gym to achieve that physique!!!"
So if you don't want YOUR hard-earned "before and after" pics hijacked by some snake-oil salesman, you might consider watermarking them or otherwise making them unappealing for commercial use. Or maybe, you don't mind your pics floating around the Internet!