Copyright information from http://www.jpl.nasa.gov/images/policy/index.cfm - Unless otherwise noted, images and video on JPL public web sites (public sites ending with a jpl.nasa.gov address) may be used for any purpose without prior permission [...]
Note: This only applies to works of the Federal Government and not to the work of any individual U.S. state, territory, commonwealth, county, municipality, or any other subdivision.