Encrypt your photos using a secret key and saved to a folder(Encrypted) as a different image file and if you decrypt your encrypted photo then you must follow decryption process and you will get the decrypted image file in the "Decrypted" folder. This app does not use any database or external file the key is hidden in the codes only.
The app saved the encrypted photos to the "encrypted" folder and the decrypted photos to the "decrypted" folder.
This app does not demage or delete any photos you have it generates a scratch new copy. Keep or not to keep your original photos is just your choice!