Understand how QR codes are made, to re-arrange the shredded pieces into a valid QR code. Then brute-force the interchangeable strips.

https://github.com/rsa-ctf/write-ups/blob/master/2018/squarectf18/C3-shredded/README.md

Original writeup (https://github.com/rsa-ctf/write-ups/blob/master/2018/squarectf18/C3-shredded/README.md).