I have photos on Bigstock. I have been on the site for a year and have not sold anything. They examine every photo that you submit and only those that meet their quality standards and are of subjects that they are looking for are accepted. Examine each photo yourself at 100% size and look for artifacts, fringing, noise, etc. If a photo is sold the photog gets very little - but, of course, every dollar helps. As the last reply said - you need to upload a LOT of photos to begin to make any money. And if the photos have any people in them you must have signed authorizations from each person in a photo to put it up for sale on the site.