hey thanks a lot that explains the way to go about it really well and sounds like the best idea.
it will save a lot of retyping when photo sizes are to be changed.
as you say an end user of a watermarked jpeg whom enlarges it, is stuck with a stretched watermark
still i'd easily provide a PDN copy along with its jpg, to give the same control to people who are using a pic of mine.
i hope to have pics small sizes for free and full size for sale
or would that be disallowed if i am selling the photos?
i haven't tried photoshop and i think it costs too much.
open-source sounds more or less only for students and isn't it a saleable art work if they use an open source ware like this?
thanks again for your interest