[id] = CopySprite(source, dest)
source and creates a copy
of it as sprite dest. If you specify Nil in the dest argument, this
function will choose an identifier for the new sprite automatically
and return it to you. The new sprite is independent from the old sprite
so you could free the source sprite after it has been cloned.
If you just want to have a new sprite with the same graphics
as your old sprite, you should use CreateSprite() instead;
it can create sprite links which are very memory-friendly, i.e. they
consume very little memory and thus should be preferred to CopySprite()
whenever possible.