How do I delete duplicate photos?

Photos that were synced from your computer are deleted by removing them from where they were synced from and then re-syncing. Only photos taken with the iPad, copied onto it via the camera connection kit, or saved from emails/wesites etc can be deleted directly on the iPad - either via the trashcan icon in the top right corner if viewing the photo in full screen, or via the icon of the box with the arrow coming out of it in thumbnail view.