I have some students who are producing some textures for V4 and M4. As they put the textures onto the models, though, thick black lines appear around places like the nostrils (almost like a toon render without it being a toon render) and one has experienced almost a mirror image of a pattern appearing in black where there is not pattern.

Any ideas what could be causing this anomaly? They are using V4/M4 textures as the working base and those appear fine on the figures. It's only after the textures are modified that this weirdness occurs.

btw: I have seen this occur before. Years ago. Can't remember what to do about it.

Thanks.

can you post a picture of the offending model and the texture image ?

This looks like bump maps that are set too strong. 

 Yes, bump- or displacement maps. Try disconnecting both :)

It could also be the problem with the texture. There needs to be colour bleeding when painting from the UVs. If your basic background colour is black then it's just the UVs stretching the black from the background texture.

Or maybe not....

Are you using raytraced shadows/ambient occlusion/shadow maps? If so, it could be a setting of one of those too