Question: At the very end when they show the sun setting over the hill, you can see something/someone moving across the screen, just under the ground. Is this done to symbolize something, or was it a sort of camera problem?
Answer: According to Ted Neeley and Norman Jewison on the DVD commentary, the shepherd walking across the frame in the final shot of the film was never intended to be there, and just happened across the shot as they were filming. Because of the significance of a shepherd in the teachings of Christ, Jewison and the crew were struck profoundly by the timing of this shepherd crossing the field, and kept the shot. They got a perfect sunset, as well as a subtle depiction of the resurrection.
Answer: Robin Hood, while disguised as a stork, wouldn't stop shaking Prince John's hand and it was starting to annoy him. Prince John was also robbed by Robin Hood earlier in the movie so he wanted to make sure that the jewels in his rings weren't stolen again.