I don’t use watermarks to prevent image theft, because you can’t prevent it. I do it only so that people can find my name or website if they like the photo. Previously I would put my round watermark logo over the image, in the corner, large enough so that it would still be legible if someone downscaled and compressed the photo, for example by posting it in Facebook. However I found that this was not acceptable in some cases, as the some photos, particularly peaceful landscapes or macros, would lose much of their charm by the contrasty logo in the corner. So instead I decided to leave the whole image intact, add on a footer, and have the brief information in there. So far I’m far happier with that.