What to do if Odnoklassniki constantly access non-existent files?

Question

Nginx

I found an error.log of 30 megabytes, with errors like:

2016/02/03 15:36:13 [error] 24493#0: *778762 open() "/path/to/image/image-280x158.jpg" failed (2: No such file or directory), client: 217.20.153.4, server: example.com, request: "GET /uploads/image-280x158.jpg HTTP/1.1", host: "example.com"

It comes from different IPs, all start with 217.20.* and belong to Odnoklassniki.
The pictures request different ones, they have in common that they are post thumbnails and are cut by the engine (as evidenced by 280x158 in the title). Approximately 1.5 months ago, the design was changed, the cache of slices was deleted, and the new ones are cut in a different size and, accordingly, have different names.
It can be assumed that there were about 200 such images before the redesign.
There are no 404 errors for users.
The site was very actively rummaged by users, incl. and Odnoklassniki.
What to do with all this?
UPD: thanks to everyone for the answers, although I expected to hear some kind of revelation about the world of classmates unknown to me - these are really solutions to the problem)

Answer 1

- (the easiest) to score, they do not create any special load.
- (the most correct) - still give pictures to Odnoklassniki.
- (if it is politically decided to break backward compatibility) - block these requests with a firewall.