I think it would be a nice feature to add watermarking on-the-fly. Just keep in mind the following:
# Adding watermark to a JPG will recompress the JPG. That means the JPG you uploaded at a fair compression, will be re-compressed when adding a watermark on-the-fly.
The way to avoid any extreme visual degeneration, would be to upload your originals at relatively high quality 90% or higher. Certainly requires some "attention"...
# Adding watermark on-the-fly would slow down the viewing experience, because before every image loads, the watermark overlay needs to be processed onto image from server. Of course, some still consider this a crucial benefit.
# Speaking for GD at least(which is globally available, unlike imagemagick), I think it can only append watermarks on images below certain size, because of server memory limit. Normally, this is something below 1280x1024 ...
temabu wrote:This would be really useful on the fly so we dont have to mess up the originals.
# Loading watermarked images "on-the-fly" wouldn't really protect your original files though just because they are not loaded into the gallery - They would still be available in accessible folders. If you wanted true protection, you would have to watermark them and overwrite. You could perhaps keep originals in some secured folder, but what reason would they have to exist if they were not to be used?