well, IF you have a professional photo displayed in full resolution for sale - it would make sense to put a watermark on it for viewing and remove it after the purchase.
as the inet photos go at 1000 pixels wide max - it's a low-res and cannot be used for any professional purposes, except may be putting it on some site (blog? on-line catalog?). which is a very minor infraction, so to speak...'cause it's hard to find and nobody really tracks stuff like that (unless you're a well known photographer and want to spend big bucks threatening with infraction lawsuit; but then you won't be putting stuff on-line left and right for free either ;)).
it's a personal choice of course, but i feel that protecting low-res snap shots is quite silly. it does detract from the picture, even the sigs at bottom 'copyright.. ' etc.
i don't stamp mine and don't watermark, but then i don't upload full photo's either ;). IF i were a pro or aspiring to such a career, perhaps i'd be more careful. but i am not and hence don't bother.
