icloud only stores photos in backups (or in a special case, when using photo stream). If you have turned on backup and made sure the camera roll is turned on (only photos from camera roll are backed up), then you can get photos back by performing a restore. But note that users should always sync photos to a computer to archive them, relying on icloud is not foolproof.
Go to Settings>General>Reset and tap Erase All Content and Settings. This will erase your device. Then you will go through the setup screens again as you did when your device was new, and when given the option, select Restore from iCloud Backup.
This link gives another overview of backup and restore:
HOWEVER... you may run into a snag, namely when the newly restored data is downloaded, an automatic icloud sync may occur that will wipe out any Apple data (contacts, calendars, etc) that was restored. If you have such an issue, read the following that describes restoring contacts. The info will also pertain to other Apple data.