It's unfortunately not uncommon for such images to appear on the Russian internet. The Youtube thumbnails are possibly things that were linked to from VK communities. Or maybe there are links in the content somewhere.

If I go on Yandex and search "img " and then a bunch of random numbers, I get almost all pictures of young women, and many pictures of underage girls in provocative poses.

This sort of thing does happen. A few months ago, people discovered similar results on Google Images(!) by searching "TV television and film". The results were being pulled from a 4chan archive of the board with that name.

I don't think it's related to the "VK" web results problem though. If you search "VK," or "VK!" or VK with any punctuation, all the web results come up as expected.

I'm unsure why this post doesn't have NSFW flag/tag/marker from the get-go.