Shadows

The shadows in this picture do not make sense to me:
http://oi47.tinypic.com/20fexq0.jpg

Also, the shadow on the bottom left appears to comport with the curvature of the "rocks" about the soil. Moreover, the shadows are not as dark as those at the bottom of some of the rocks in the middle (look at the arrowhead-looking rock). They seem to be closer the same color as the darker shade of Martian soil than they are to shadows.

Why are the back of the wheels so bright?

Could these "shadows" be associated with Martian microbes/biology?

Source:
http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/00064/opgs/edr/rcam/RRA_403163979EDR_F0050104RHAZ00309M_.JPG