If you mean you have duplicate photo's in folders on the hard disk, use your favorite file manager (such as Windows Explorer) to delete the unwanted copy. Deleting pictures is no different from deleting any other file: right click>delete or the delete-key.
But maybe you mean something different?
Kees
Now add some detail so that smart CNET users (like you!) can answer. If you're lucky, a CNET editor might choose your topic for a How To article or video.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic