Stock photos are licensed photos captured by photographer with the intent to sell them or provide them publicly for art work usage. These photos are licensed and copyrighted to the one who captured the images (Photographer), stock photos are available for download with a paid fee and sometimes free, depends on the requirements.
Sometimes the stock photography images are available for rent or commercial usage and can be priced up to hundreds of dollars depending on the type of photography and the resolution. A mid resolution stock photos are available in between the price of 1$-100$.
There are tons of websites providing free stock photos as well as individual photographer who are willing to trade stock photos with you online. This is much like a digital business of photography, though the best stock photos depends on your need and the money you’re willing to put on these images.
Royalty free stock photos – These are stock photos that can be used again and again for multiple use. You have to pay one time fee to own such stock images and then the you have the exclusive rights to use it multiple times on your brochure or for any purpose.
You can find various forms of stock photography in forums, art websites and designers sites such as deviant art that are free or if you are willing to own rights of stock images then check out commercial stock images website such as istock, big stock photos and so on..