Should be pretty simple..
Give the photo's drag and drop behaviour and instance variables OldX and OldY
On drag and drop start
> set OldX to object.x
> set OldY to object.Y
And "On drag and drop drop" compare the OldX and OldY with object.x and object.y or Mouse/touch.x and Mouse/Touch.y and decide which actions to take accordingly..
I told my dentist I had trouble with my teeth and asked her to fix it without looking in my mouth..