The Jupiter moon found in Voyager 2 photos that was the first moon discovered by an interplanetary spacecraft was Adrastea.
David C. Jewitt and G. Edward Danielson identified Adrastea in Voyager 2 images taken on July 8, 1979. It appeared only as a tiny point, but the discovery established a new method for finding natural satellites: examining photographs returned by a spacecraft rather than observing from Earth through a telescope.
Adrastea is the second-smallest-distance moon from Jupiter among the four inner moons and orbits at the outer edge of Jupiter's main ring. Its orbit takes only about 7 hours and 9.5 minutes, shorter than Jupiter's roughly 10-hour rotation. The moon is thought to supply much of the dust in the main ring.
A common mix-up involves Metis and Thebe. Voyager 1 images later revealed those moons in photographs taken months earlier, but Adrastea was the first moon discovered by an interplanetary spacecraft. Amalthea, by contrast, had been discovered photographically from Earth in 1892.