Ken, I feel much the same about pinterest users "stealing" my pictures. But that was done long before pinterest came along just as well.
E.g. I still have a drawing of mine that's used (modified, but clearly a copy) without permission by CNN on their website - they don't even bother to answer to emails.
Sure they added to it - but the basis was stolen - unlikely they stole it from me - they probably got it from somebody else who neglected to mention (s)he stole it from me.
I can prove it as I have the original images in higher resolution ...
It's also a reason why I tend to not put most of the pictures I like online unless I have to.
BTW: if your pictures are *good*, try selling them as stock pictures.
But aside of the obvious copyright problem, even those that do not care about the copyright of their pictures and are just trying to sell physical goods might be in trouble with their customers switching from a physical collection to a virtual one ... even if you just sell collectibles via e-bay ...