If they're deleted on the device yuo want to retrieve them from, and you had Photo Stream turned on, then you should be able to get them from another device or computer. Also, it's recommended that photos be synced to a computer frequently (if you take a lot of shots) via USB. The final method is to reset the device and perform a restore. This assumes the photos were in the camera roll. However many users have had problems retrieving photos via a restore. I'd say, if you didn't sync the pics to a computer or don't have Photo Stream active, then the pics are gone.