Rating: 5.0

The challenge is a black-box reversing challenge where we have to reverse-engineer an image format. Experimenting with one-dimensional rows or columns reveals a binary tree structure, and after examining the bits set in some important bytes in the format, everything is revealed to be a quadtree. Read the details here: https://blog.vero.site/post/proprietary-format

Original writeup (https://blog.vero.site/post/proprietary-format).