The image to the right depicts Nereid, Neptune's third largest moon, which orbits very far from Neptune and therefore was not seen close up. On the right is tiny Despina, a moon that orbits close to Neptune and is only about 150 km across.
Finally, here is Despina, transiting the disk of Neptune. This is a montage showing Despina and its shadow at four positions, each taken nine minutes apart. The last one shows Despina itself against the clouds of Neptune.
Finally, here is a version of the transit image with Despina artificially brightened to aid visibility.
Processed images Copyright Ted Stryk, Raw Data Courtesy NASA/JPL