Let's be real. The way I look at it, take a picture and go try to do what I do. I can't even reproduce one of my own collage for a customer. It's pathetic, really. And, to be really honest here, if your work can be copied from a photograph, made and sold, you're doing something wrong. It shouldn't be that easy. You need to up your game.
I think it is a real problem for photographers and 2d artists because, apparently, there are cameras so sophisticated, they can take a photo of a photo and then reproduce it at will. That would stink, I agree. Those artists should have as many of those obnoxious little signs all over the place as they wish.
But let's also be real about "theft" of intellectual property. There is nothing new under heaven Horatio (or something like that). It's all been done somewhere by someone. Did that great idea come directly from your brain with no input from the outside world or did you notice something interesting in a gift shop in Idaho one day on vacation and that image percolated in your brain for 2 years to be born as an aspect of your own work? What do you think?
I shamelessly stalk the web sites of artists that do what I do. I steal from them. They inspire me. This, for instance, from the Uncommon Goods site: