Photo or note recovery requires that you have properly backed up your data.
See: How can I back up my data?
If yes, you can do the following to recover your photos:
1) Launch OI Safe. Instead of creating a new master key, click "Restore" when being asked for a new master password. This requires the "oisafe.xml" backup file to be on the SD card.
In case you have created a new master key before restoring the old master key, please note that with the old master key, you will not be able to see the newly encrypted pictures, so it is recommended to decrypt all pictures first, then restore the old master key, and then encrypt all pictures again.
2) Use your old master password to recover your old passwords in OI Safe.
3) Then you should be able to recover your notes in OI Notepad and your photos in Obscura again. (You may have to turn off your phone and on again before they are recognized).
Alternatively you can use MyBackup Pro to recover your OI Safe passwords and your master key. Then you should also be able to recover your photos and notes.