Attached is a script that will Randomize your Materials, be it built in, or image maps, it doesn't care.
Sample image shows a completely inane and useless image for this purpose, yet, it should get the point across.
Think of a wood fence that is weathered, but you only have a single map for overall weathered consistency. This will give a randomized appearance to it all looking far more realistic.
Included in the Zip , Folder to install (Compiled and support files),the Source Code (.fsl file), Test file (not pointed to any graphic) and some other stuff.
The script is $1,000,000 for those who can afford it, otherwise it is free.