Which 'photo vault' app ? If Private Photo Vault (https://geo.itunes.apple.com/app/private-photo-vault-pic-safe/id417571834?mt=8)
The first time you used Private Photo Vault, you were prompted if you would like to create a recovery e-mail address in the event you forgot your password. If you entered your e-mail as a recovery address, you can recover your password. If you did not setup a recovery e-mail address, you can’t recover your password.