The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter took this image of Phobos from a distance of about 6,800 kilometers (about 4,200 miles). It is the second smallest moon in our solar system.
From www.Geology.com:
Phobos has a heavily cratered surface. Its most obvious feature is a large crater named "Stickney", shown here on the right side of the image. The craters are of various ages. The youngest craters have very crisp rims and a distinct crater shape. Older ones have more subtle rims. The oldest appear more as "dimples" rather than craters.