What is the difference in cats of an altered male and unaltered female?

Whether a female is spayed or not isnt' visible once the incision heals.

A non-neutered male will have large testicles, and a neutered male will have small, fuzzy sacs where the testicles were before removal.You can tell a fixed male from a female because a female cat's rear will just be the anus, whereas the male still has a scrotum and penis which look like fuzzy little balls below the anus.I'm not sure where you'd find pictures of this, but it's really easy to see.