Images presented on NSSDC's Image Catalog are in the public domain and rights to the image are not held unless otherwise noted. Public domain images may be used for any purpose that does not imply an endorsement by NASA. If possible, please acknowledge NSSDC as the supplier of the data. In addition, where the source of the image (by project or as a specific person) is credited in the text, that should be acknowledged as well.
If you cannot find the image you are looking for on the Image Catalog, try this list of other sites. The list is not a comprehensive listing of all sources of images, but covers the areas we are asked about most frequently.