Obligatory reference to Gödel, Escher and Bach.

(For the record, I do understand this article explores a different mathematical aspect of Escher than Hofstadter)

I've seen Lenstra's talk about Escher's print gallery some years ago in Rome and then again after a few months in Pisa.

One of the most captivating talks I've ever seen. He's a great speaker. I wish I had him as a professor.

EDIT: forgot to add, in the Mathematica blog there is another explanation of the mathematics between the "Droste effect" and the code to obtain it: http://blog.wolfram.com/2009/04/24/droste-effect-with-mathem...

I'm just speechless about that computed re-creation assembling the four frames. Brilliant.

The interpretation of the blank spot is also quite nice and very Escher-esque, with the content literally jumping out of the frame. Probably Escher left the center patch blank because his construction method would have him exceed some technical/physical limitation, so instead of drawing an approximation he preferred a void.

There's an OS X screensaver based on this work which animates the effect, in a similar way to "dive" animations into fractal images. Fascinating but also nauseating after a while.

http://wakaba.c3.cx/s/lotsablankers/lotsaescher

As someone who grew up mesmerized as a little kid by a large framed work by Escher in our house, this is an awesome read. :)

Thanks! Awesome read! Makes me love Escher's work even more.

Does anyone have a larger version of the last picture?

Here's a slightly larger version (thanks to http://tineye.com): http://netdna.webdesignerdepot.com/uploads/droste/escher4.jp...