Can't delete certain photos. Tried unsyncing from iTunes, but that doesn't help.

How did the photos get on the iPad ? If they were synced from a computer then they are removed by changing your photo sync options and re-syncing. If you want to remove all synced photos then try selecting an empty folder on the Photos tab when connected to your computer's iTunes and sync that - is that what you are trying to do, remove all synced photos, or just some (and is that the computer that they were originally synced from) ?