The pattern in the logo, behind the home page title and in the footer isn't an image. Code draws it every time the site is published, and every publish draws a different one.
Truchet tiles
The idea is over three hundred years old. In 1704, Sébastien Truchet studied what happens when you fill a surface with a single tile rotated at random. The version I use is the simplest: a square with two quarter-circles in opposite corners. Each tile has only two possible orientations, but once you lay them side by side the arcs join up into paths, waves and shapes nobody drew.
Where the randomness comes from
True randomness would mean every visitor sees a different pattern, and it changes on reload. I didn't want that: I wanted the mark to be stable, but alive.
So the randomness comes from a seed. Any piece of text becomes a number (via an FNV-1a hash), and that number feeds a tiny pseudorandom generator, mulberry32. The same seed always gives exactly the same pattern.
The seed is the commit the site was deployed from. While I don't publish anything, everyone sees the same mark. When I ship a change, a new one appears.
One function
Everything comes from the same function, about forty lines with no library: the menu logo, the home page background, the footer, and the images that show up when you share a link. Each blog post also uses its own name as the seed, so every post has a pattern of its own that never changes.
The home page has a button to regenerate it with a random seed. Try it: none of the ones you'll see were drawn by anyone.