I guess an income to me would be $500 per week absolute min.
I have been shooting stock for about a year and a half now, my collection is a variety of photographs and 3d images. I first started with shutterstock, I then started submitting to dreamstime and istock, I was fairly happy with the return. After researching a bit I then stopped submitting to RF sites and moved to Alamy submitting new images as RM. After about 9 months there, many images, and not many sales I recently decided to change all those RM images to RF on Alamy and am in the process of submitting them to Shutterstock, Istock, dreamstime, Fotolia and 123rf, I am already seeing MUCH better income.
My advice is to work hard, don't EVER expect to get rich fast! it simply won't happen unless your pumping out 50 high quality images a day. It will start slow. Think of it more like a job where you work long and hard now and get paid well later. I feel it pays similar to a normal job in the amount of hours per dollars ratio, it's just the fact that you don't get paid straight away.
Thanks.