Wirt writes:
> That watermark (which is normally done by writing some sort of
> signature into the low order bits of an image, across many
> pixels, so that it can't really be seen in the image) lasts
> exactly as long as the image is not manipulated in any manner
> (made larger, smaller, cropped or converted into another
> graphic format). At that point, the watermark is gone.

Actually the DigiMark stuff is pretty good.  You can embed a watermark, then
crop the image down to 1/5 the original size, then scale the image up by
some arbitrary amount which causes resampling of the image, then print it
out, then scan it back into a file, and the watermark can still be
recovered.

G.