This person was struck several times in the head and face with a hammer, which resulted in the deposition of numerous bloodspatters on the wall behind the couch.  The black lines are strings placed along the long axis of individual stains.  The point where the strings converge indicate the victim's head was near that area as the blows were struck.  This information combined with estimated angle of impact allow the investigator to determine an approximate location from which the spatter originated. 

Click Here for a brief animation.