The smallest shadow is Io's. The shadow at Jupiter's left edge is Ganymede's. The shadow at the right edge is Callisto's. Callisto would be a few inches off to the right of its shadow.
Back in 1988 I had a program called MacStronomy for my Mac Plus (my third Mac!) that I used to recreate Jupiter's position in the sky in the winter of 1609-10 when Galileo first observed Jupiter's moons. I noticed that the yet undiscovered planet Uranus was only a few degrees away, and easily bright enough to have been visible in Galileo's scope. It was one of the brighter objects in that part of the sky. Was Galileo the first to see Uranus? Unable to resolve its tiny disk, he would have thought it to be a star.
I had a little note on this published in Sky & Telescope in February 1988.