how can I retrieve deleted photo?

Restore from iTune or iCloud backup if you have one done recently.

Do you backup to iTune (computer)?

iPad Photo Recovery: How to Recover Deleted Photos

http://www.iskysoft.com/iphone-data-recovery-mac/ipad-photo-recovery.html

How to Restore Lost or Deleted Files from iPad

http://www.iphone-ipad-recovery.com/recover-ipad-mini-files.html

How to Recover Deleted Files from iPad

http://www.kvisoft.com/tutorials/recover-deleted-files-from-ipad.html

iSkysoft Free iPhone Data Recovery

http://www.iskysoft.com/iphone-data-recovery/

Recover iPhone/iPad/iPod touch lost data, Free.

• Free recover iPhone/iPad/iPod touch lost contacts, photos, videos, notes, call logs and more
• Recover data directly from iPhone or from iTunes backup
• Preview and recover lost iOS data with original quality

 Cheers, Tom 😉