Still not got an answer to my question.

If I have not set the "No nudity" filter why should I be upset by nude thumbnails. If I set the "No Nudity flag, they are all gone, so no problem.

I would rather see an enormous boobs thumbnail and pass it by than click on an eye or a toe and then be presented with a full sized image of something I didn't really want to look at.

Why can this not be achieved?

Cropped and altered thumbnails are basically a deception.