Unusual Mars Picture

I came across these Mars pictures. My first impression is that this is a skull with some sort of helmet still on. But I'd like to hear what you guys think.

These are from Spirit's nav cam- Sol 1396

Left Shot Closeup

Right Shot Closeup

Full View

The originals are here:
marsrover.nasa.gov...

After looking over the image in photoshop, it looks to me as if the anomaly is actually just a rock.

Look's like a stone to me aswell.

But dont give up looking good work.

Take care.

Regards
Lee