It would also help to know the approximate age of the surrounding areas where this was found. And to know the type of Rock (Sedimentary being the most common for imprints like that).
I looked at the new photo's... and I still can't tell. It could be a fossil, or it could be inconsistencies in the rock. Also, I don't normally expect to see nodules and pockets in the type of rock which forms fossils, but I don't think it's "impossible", only less common.
We have a member who is a professional Geologist. He may be able to help.