Photo stream photos don't count against your storage so deleting those won't help. Camera roll photos are included in your iCloud backup, which does use your storage. To turn these off, go to Setting>iCloud>Storage & Backup>Manage Storage, tap your device under Backups, then turn Camera Roll to Off under Backup Options.
If you do this you will no longer be backing up your photos to iCloud. Be sure to import them to your computer for safekeeping so you don't lose them, as explained here: http://support.apple.com/kb/HT4083.
This article may also be of interest: http://support.apple.com/kb/ht4847.