The difference is in the intent
If you take the original and make a copy of it, then you can call it a copy, a reprint, a reproduction of the original object.
It has to look like the original object.
Those copies maybe good or bad.
However, if you present your copy as a copy/reporduction/reprint etc, then it is OK.
As long as there are no copyright to the item, you may even sell the copy as a copy.
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However,if you try to sell your copy as the original item, then it becomes a foregry.
that's because you are mis-representing the object as something it isn't.
object = work of art, coins, stamps, even first editions.
hope this is clear,
regards
Yoram