I had thought I had read somewhere about the challenges of designing a unique and valid puzzle (so that pieces couldn't fit together that shouldn't fit together

I had thought I had read somewhere about the challenges of designing a unique and valid puzzle (so that pieces couldn't fit together that shouldn't fit together) with the note that puzzle manufacturers apparently made new puzzle piece grids for each puzzle. I was pretty sure it was on kottke, and instead I found the exact opposite of that, with a link to the following project of mixing pieces together from puzzles to create surreal artwork: https://puzzlemontage.crevado.com https://puzzlemontage.crevado.com