The most affordable license type for stock photos is royalty free (or RF). Royalty free means you can use the image multiple times, without paying a royalty. This is the best choice for budget-minded designers and marketers. The downside of royalty free is that RF images are non-exclusive, meaning anyone can purchase and use them. Royalty free images have the most lenient permissible uses for both commercial and personal projects.
A rights managed (or RM) license gives exclusive, time-limited use of a stock image. Exclusive use means that only the licensee can use the image for the period specified in the license contract. RM licenses are granted on a pay-per-use basis, meaning the stock image can only be used for one particular project, only for a set period of time, and often only in certain geographical areas. Rights managed images are expensive to license, but they offer protection against brand dilution (due to competitors using the same image) and allow for larger print runs.
Extended / Enhanced licenses
Some stock photo companies allow you to purchase an Extended or Enhanced license that extends the permitted uses of a previously licensed work (usually royalty free). Extended licenses give you permission to "extend" upon the uses granted in the original license. These uses may include increasing the number of copies showing the image, use it for resale purposes (print-on-demand, calendars, t-shirts, greeting cards, etc), or allow for other methods of distribution and use. Uses vary from company to company, so be sure to read the licensing agreement in detail.
Products in the editorial collections are licensed with restrictions on usage, such as limitations on size, placement, duration of use and geographic distribution. Editorial products must be used in an "editorial" manner, which means use relating to events that are newsworthy or of public interest. If you wish to use an image or video from an editorial collection for a non-editorial use, you must normally contact a sales representative of the stock photo site to assist you.
Flickr Creative Commons
Many Flickr users have chosen to offer their work under a Creative Commons license, and you can browse or search through content under each type of license.
See http://flickr.com/ for full details
"Creative Commons is a non-profit that offers an alternative to full copyright."
You let others copy, distribute, display, and perform your copyrighted work – and derivative works based upon it – but only if they give you credit.
You let others copy, distribute, display, and perform your work – and derivative works based upon it – but for noncommercial purposes only.
No Derivative Works means:
You let others copy, distribute, display, and perform only verbatim copies of your work, not derivative works based upon it.
Share Alike means:
You allow others to distribute derivative works only under a license identical to the license that governs your work.