This is a mathematical jigsaw puzzle! You have a photo cut into q×q
pieces, where q is a power of a prime p. Therefore it represents the
vector plane over the finite field
Fq with q elements.
These q×q pieces will be presented to you in disorder, result of a
(hidden) affine transformation
of the plane. And your goal is to recover
the image by finding the inverse affine transformation. You have the right
to multiple tries in order to do it.
Recall that an affine transformation is a linear transformation followed by
a translation. All are operations over Fq.
You may play this game even without understanding the mathematics behind.
In this case don't go further than q=5;
the game risks to be very frustrating.
We also recommend another online jigsaw
Shifting puzzle which requires much less mathematical background.