One of the most challenging aspects of creating an advertisement is making it visually appealing. To address this, marketers often purchase graphics, such a pictures, from companies that specialize in offering this service (often called stock photo services). For instance, iStockPhoto.com, is a well-known company that offers a large graphics collection.
However, acquiring graphics can be quite expensive, sometimes costing well over $100 for a single image. But, as discussed in this story, if you are advertising on Facebook, you now have an exceptionally cheap way of using graphics for promotional purposes. In fact, it may be free. There does seem to be one significant limitation: the graphics must be used for ads appearing on Facebook.
Image by S1m0nB3rry