..:: What is stock?::..  
..:: Microstock agencies::..
Stock photography is about selling images online.
More specifically, selling the license to use a photograph.
Stock photographs end up in magazines, books, on webpages, as wallpapers, etc.
With stock photography, a picture can be sold many times. This means the sale price can be relatively low but the quantity of sales high.
Typically, the stock agency takes the bulk of the sale price and the photographer collects a royalty for the sale. As for why you should care - as a photographer’s collection of photographs gets bigger and bigger, this can turn into a full-time job.

If you want to get back the money invested in your photo equipment, you can achieve that dream at one of the following stock agencies. You can become a microstock photographer.