The problem I have with 'stock' are the micro and free stock sites. I sell stock directly and try to take the middleman out of it in order to make more than a few pennies on my images.

The degree of success depends on how unique your images are or how specific the client needs are.

If you ask me for 58 different breeds of cats, with each breed including several varied, allowed colors - I can help you. If you ask me for a Solid Black Persian on a white background, I can help you. There is value in that.