Ask HN: Algorithm behind Windows thumbnail preview?

Hopefully it is not too offensive to the audience. Just aiming to satisfy my curiosity.

I was printing a Word document where I entered a picture with complex patterns. When hovering on the Word icon on the taskbar (windows 10), it shows a preview thumbnail. However -- whatever algorithm is used-- it compressed the image so that the preview showed a remarkably different image. I thought it was neat and wanted to figure out what's behind it, or at least some pointer. For no reason.

Since I'm not even sure where to start finding this out, I thought I'd ask. Is HN the right site for this? I guess I'll find out!