This is the issue from [https://www.mediawiki.org/wiki/Topic:Sm8fzlwah19ml143] .
After I upgraded my mediawikis into mw-1.25.1, When I make upload images, mw itself unabled to make thumb files into /images/thumb. In one of my wiki, even /images/thumb directory itself do not exist. When I make appropriate directories and make thumb files - it works. But after I updated one of wiki - opened one - into mw-1.25.2, the same problem exists. so I think that these problems connected with 1.25 releases itself. Images when I uploaded during mw-1.24.1 normally shows thumbnail files which was requested previously(If you see http://wiki.ellif.10g.kr/%ED%8C%8C%EC%9D%BC:Yuireil_omoromaci.jpg, 320px and 800px thumbnails exists, but another thumbnails does not .