Another guess here, but it could have been crowdsourced using Amazon Mechanical Turk. Assuming a conservative 0.05$ by picture, the total cost would be 901 * 0.05 = 45.05$.
Yeah, this seems likely. Here's how I'd do it: create a webapp similar to this one to show to your Turkers. The difference would be that it would show an image at random, and the Turker would decide whether or not someone is pointing in the image, and if so they would click where the person was pointing. For each image, take the mean position of mouseclicks. This becomes a seed for the Voronoi diagram.
You can tell he/she "cheated" a bit for some the parts of the canvas that didn't get many seeds. For example, if you move your mouse within one of the large cells in the bottom left, the image just moves to keep up with the pointer. :P
