That's it. WHen you launch this mod in a 1.7.10 server, this error is shown:

java.lang.NoSuchFieldError: images at lain.mods.skins.OfflineSkins.<clinit>(OfflineSkins.java:125)

This mod is Client-Only, you don't need to install on server.

That's what author said in the post :)

Another thing, this mod didn't support 1.7.10