We have an album like below:
User drag picture 0 and drop it on picture 3. There will be a menu which has a "Put back" action.
After click "Put back", picture 0 will be behind picture 3. The order of all the pictures will be recorded in database.
I added an action in View-Sort Items, which is called "By Manual". User can restore the manually sort result by click on "By Manual".
The code can be found here.