That's a good point I didn't really consider. Here're the resulting file sizes.

The triangles used a larger image as a starting point though.

   75K image-previews-adaptive-blur-output.jpg
   13K image-previews-gaussian-blur-output.jpg
  9.1K image-previews-plain-blur-output.jpg
   55K image-previews-input-1.jpg
   52K image-previews-probability-triangle-output.jpg
   61K image-previews-wave-gradient.jpg
   79K image-previews-rippled-output.jpg
  300K image-previews-circle-map-blur-output.png
  373K image-previews-output-with-triangles.png
  461K image-previews-output-with-probability-triangles.png
  1.2M image-previews-transparent-triangles.jpg
  217K image-previews-plain-blur-lg-output.jpg

The impetus for this was to create a less blurred, more coherent preview image that is not the original image. Why is that? I suspect to entice people to want to pay for the images that are being previewed. The question is now: given there are different techniques, which techniques lead to a higher rate of purchases of previewable content (right)?

That's a good point. It would definitely be worth A/B testing the results.