
Cue everyone saying "don't do it"
I agree with the masses, by the way, though. Watermarking (depending on style, size and placement) can ruin photos, and really the best defence against use is simply to limit resolution. I use a max side of 500px on my site. People can/may use photos from you then, but not for anything particularly useful. A discrete watermark can be removed with comparative ease and little skill nowadays anyway.