It's not easy for the average person to just dump snapshots on iStockPhoto and make money. You really need a DSLR to begin with (though I have gotten photos approved and sold that were taken with a Canon S3 IS), good composition, and interesting subjects. You will also likely need to spend some time in Photoshop on most images. So if you're looking at a startup cost, that's a bare minimum of $1k for camera and lens and likely $700 for Photoshop. (You could try free image editors though.) If you're shooting indoors at all, add at least a few more hundred for lights, reflectors, stands, screens, etc.

After all that, there is a lot of competition on the site. Being active in the community there helps a lot. I doubt he got to 13k downloads by just posting photos and waiting for downloads.

His photos look professional, they are linked from his web site. I guess you have to find the right niche, as in other business endeavors.

Thanks. I am doing all my best to make my phots. It cost not only a lot of time in post processing but I have invested a lot in photo equipment and software. But it can pay back if you know what are you doing...