If they were photos that you synced to the iPad from your computer then they are removed in the same way as you put them on the iPad i.e. select the iPad on the left-hand sidebar of your computer's iTunes (with iTunes 11 you can enable the sidebar via option-command-S on a Mac, control-S on a PC) and then on the right-hand side of iTunes use the Photos tab to select which synced folders/albums that you want to remain on the iPad - you can't see or remove individual photos, it's done at the folder/album level.
If the photos were taken with the iPad, copied to it via the camera connection kit or saved from emails/websites etc then that can be deleted directly in the iPad's Photos app - either via the trashcan icon in the top right corner if viewing the photo in full screen, or via the Edit button in thumbnail view. You can also import those photos to your computer and delete them as part of the import process e.g. on a PC you can use the windows camera wizard, on a Mac you can use iPhoto, Aperture and Image Capture : copying photos to a computer.