Using an image of a face or upper torso & head (human, and evidently apes & monkeys) has a positive effect on CTR --on my sites it's at least a full percentage point for humans and -judging from the 'Punch the Monkey' and 'Bonzi' campaigns- 3 to 5 percent for our cousins.
Compaq has a new "put crosshairs on cpu" copycat of style and there is a "click the shopping cart" one, now, but I'll bet the ctr is lower than the monkey. BTW, every post I've ever seen on PTM says that he gets 8 percent ctr --that's ten times the average.
It appears I'm going to become the "All Bonzi, All The Time" site... not that I'm complaining with the $check, but that purple gorilla is now buying 66% of my brokered inventory. His CTR, btw, is averaging over 8% (note the lack of a decimal point in that CTR).
The good news is that he's holding my default rate down to 15.6%