A friend of mine takes over 200 pictures a day of just random things. He does all this on his Iphone not even a great camera. He then throws his watermark on it and throws it on his site, after people know where to go to see your work they will come and look. Offer wallpapers for .99 cents. Also people are always looking for pictures, submit them to numerous sites. I know national geographic and places like that actually buy pictures from you.
He makes over $300 / Month and that is without advertising his site, and just uploading pictures, and selling them for .99 cents. He does not submit them or look for people to buy them, he just lets them come in as they please. So i am sure you could make a living off of it if you invested more effort in finding buyers than he does.