The images are allowed to be treated as being in the public domain.
However, crediting to "NASA / JPL-Caltech / SwRI / MSSS / Gerald Eichstädt" appears appropriate.
Add your name or data sources to the credit list, whenever you create derived works.
The referenced images are large (more than 6000 x 8000 pixels, up to more than 20 MB). The zip files are up to more than 146 MB each. Consider your data transfer volume costs and your system restrictions, before clicking on an image.
Downloading, and distributing the files is on your own risk.