Stock photo services are not much of a viable income source. There was a time when a photographer could generate some income but I overwhelmingly pull in .25 cents per digital download of my photos. That’s all. Additionally, there’s the problem of some anonymous person somewhere who gets to accept or reject the photos I submit. There’s no regulation of this. It’s entirely subjective. I’ll have photos rejected one day that are accepted another with no changes made to the image. I believe there was a time when stock photography was good to the photographer but I think those days are gone.