I don't know how the coordinates were defined for the 900 images. They might have just copy-pasted pixel readings from some image program like ImageJ for half an hour. At first I thought they used html area tags to define bounding coordinates for a number of circles or rects around every image coordinate, but in functions.js there's VoronoiGrid.js. I had never heard of that - it separates all of the coordinate points so that every image they used gets displayed (every image gets its own "puzzle piece" of pixels it will be retrieved for: no two images are in the same bounded area).