[Luyt]

The starting strip is, by definition, the strip on which no other strip has been placed left of. There is no other way of determining what the starting strip is; it's not a given. The problem is that with my current pixel matcher (sum of absolute differences) one strip is wrongly attached. That made me think I also have to take other features in consideration, like color, hue and/or line detection. But that seems outside the scope of this challenge.

The algorithm works fine for some random pictures I found on the web. It's just not working for the Tokyo picture ;-(

[webfuel]

Minor spoiler/hint:

My algorithm, given a strip, would tell you which strip was on the right and also gave a certainty. The last strip would have a "next strip" value shared with an earlier strip (thus wrongly attached) but with less certainty.

Edit: Or (worst case) the last strip would have a high degree of uncertainty.

[asharp]

That's what stable marriage is for. With some reasonable heuristic it should just give you the best partial ordering, which when flattened into a total ordering should give you the most likely picture.

How do you calculate your certainty?

[Luyt]

Currently I'm using a matrix to determine adjacency, but I'll give this graph idea a try. Thanks for the tip!

PS. Have you actually realized a succesful implementation? (Just curious)

[webfuel]

No problem! Yes, I have this working:

http://webfuel.org/instaunshredderv2.php

It also works on the test images I created:

http://webfuel.org/a.png http://webfuel.org/b.png http://webfuel.org/c.png

[s3ththompson]

This is exactly how I implemented my solution. The worst case scenario is important because some images have last strips that have a unique "next strip" value.