You've also got to rememberto put some text in on the reverse side and give it just the right amount of bleed through.
I once got the Guardian's spot the ball competition (this was years ago), scanned in the side with the image on it and also the other side. Reversed the other side and then took it away from the image side, just the right amount (I think it was something like 8%) and then I did a edge detect on it, found the bit that had different frequency characteristics (ie, was smoother - indicating where they had pasted the background into the image), took the centre of that as where the ball was and won the competition.
(,
Wed 3 Mar 2010, 20:42,
archived)
I once got the Guardian's spot the ball competition (this was years ago), scanned in the side with the image on it and also the other side. Reversed the other side and then took it away from the image side, just the right amount (I think it was something like 8%) and then I did a edge detect on it, found the bit that had different frequency characteristics (ie, was smoother - indicating where they had pasted the background into the image), took the centre of that as where the ball was and won the competition.
