See some common terms used with images below:
Stock Photos: Professional photographs of common places, landmarks, nature, events, or people that can be used and reused for different design purposes. Some stock photos must be purchased individually while others can be used royalty free.
Royalty Free (RF): Users pay a one-time fee to use images multiple times on on multiple projects.
Rights Managed (RM): Users pay fees associated with each use of an image. More restrictions may apply.
Creative Commons (CC): These licenses provide image creators a simple, standardized way to grant copyright permission to their work. Check the license to see how the work can be used. A number of licenses exist with varying levels of protection. Be sure to cite these works with the creative commons license as appropriate.
Images are governed by copyright law-- just like journal articles, books, and other print or digital materials.
Is the image I want to use in the public domain?
Is the image covered by a license that allows me to use it? (See left box)
Is my proposed use infringement or would it be considered Fair Use?
Can I obtain permission to use the work?
Need to find where your image came from?
Source: http://unitproj.library.ucla.edu/col/bruinsuccess/03/02.cfm