Piston Slap or Engine Knock?

I own a 2007 Chevy Malibu LS 2.2L 4 Cylinder Automatic.  When i start the engine
while cold, there's a knocking or slapping noise.  It only happens when it's cold and as
the engine warms up it slowly goes away, i just want to figure out if it's piston slap or if
the noise is being made by something worse like a bad rod or sparks or broken valves.  
Ideas?  (btw i'm 17 so my knowledge is limited) (My car is the one on the left in the
picture)