Disclaimer: This could be caused by me using an outdated Steam version, that does not include the new library design.
Problem:
In the Steam library, the picture showing for the latest reached achievement is only showing a small portion of the actual image; by my estimation 1/16th.
Every other place where achievements are showing (activity feed, achievement screen, layover) does show the correct image.
This is happening since the new three achievements (505, season, books). I do not experience something like that with any other of my games.
As I said, it could either be, that since the last achievements (nov 19) there was another change in the library design, although the Steam interface change dates back further, or maybe you included wrong files for this specific image type.
So far it still looks the same as above, so not fixed yet.
Of course it could be, that I’d have to delete some temporary files to get a correct image, but from my experience, these do not tend to get stored this way (and also getting to Steams temp files is a pain in itself).
[Edit:] Nope, that didn’t do the trick either.
Just cleared an achievement in a different game, that has been included yesterday, and it is showing normally, so this is definitely something exclusive to GoW and not a general issue with my Steam.
My best guess is, some files were uploaded in the wrong resolution. Also a small correction to what I said above: It’s also happening with the images in the ingame hub.