I tried to find this texture in my texture folder, but there are simply to many of them. It would take me a lifetime to do that.
Any ideas?
Yes - check the meshes! Open a head mesh in NifSkope and see which textures are related to it.
If they look like that, then it really is a prank. If they look fine, then it's just a case of bad UV mapping or something like that. Maybe there were textures included that were supposed to go on the vanilla head mesh, but since you're using Rhedd's head mesh, the UV mapping doesn't fit any more. Or something like that.
In any case, THOSE are the textures you want to get rid of.
Are you sure the pack you installed contained nothing but textures? No meshes at all?