Yes 1-st step it's background-image: url("../img/body.jpg"); like wrote Vladimir, but you should remove some other bg too:
common.css at line ~ 35
thenCode:Only registered members can view the code.
common.css at line ~44
thenCode:Only registered members can view the code.
common.css at line ~51
remove backgrounds for this styles.Code:Only registered members can view the code.