I've had some luck by doing this, it seems, wrongly.
I had a base layer which I made two colors, then a new surface layer where I added a image on the layer.
I added next a surface shader, fake rocks.
On the one, I see that I had no control over the rocks where they went, and it looks awkward to see them climb up one side, but I wasn't sure how to solve that. The second, there wasn't that problem.
Now I have tried it the correct way, but not with as good results as seen here. Making the color white didn't seem to help, but ticking turn off color did...