I wrote a blog post about QR codes with an overview of image techniques like this and a bunch of links to different implementations if anyone would like to see more things like this.

https://kylezhe.ng/posts/crafting_qr_codes#image-techniques links directly to that section and skips the fluff about how QR codes work

I highly recommend checking out https://cgv.cs.nthu.edu.tw/projects/Recreational_Graphics/MQ... which uses word clouds with QR codes and looks crazy cool