We had some interesting discussions about how to best do it - jedberg@reddit had one of the cooler ones that involved building your own decoder to pass over the obscured text. In the end, Randy suggested a discrete Copyright-esque position and font that was a simple, elegant solution.

The Dr. McNinja books just put the image title text at the bottom of the pages.

That's pretty clever. I agree that sometimes though, the simple approach yields a better solution :)