The twin Voyager spacecraft went by Saturn in the early 80s and imaged several moons. During the recent 10 years, Cassini has orbited Saturn and imaged the same moons many times with greater coverage and detail. Here is the link to a web page from Jet Propulsion Laboratory that shows the level of detail before and after of those mission images. This screenshot below is also linked to their web page. You must visit their web page to view the images.