Running Randomizer.jar will randomize all 16x16 images in all subdirectories of the working directory of the jar file.
To use this to make a resource pack, extract the .jar file from your minecraft version (e.g. 1.8.9.jar) which can be found in the minecraft versions folder. Run Randomize.jar in the textures folder or any above folder to randomize textures. This can be done repeatedly.