The best way to hang pictures on stucco and poured concrete walls is with a concrete screw. These screws are designed to grip the concrete while supporting the weight of the picture. The longer the screw, the more weight it will support. The best tool to drill the hole in the stucco is is a drill equipped with a masonry drill bit. The drill's sharp tip will easily penetrate the poured concrete without chipping the stucco that covers it.
Tape over the point you will drill an "x" made out of painter's tape. The tape will protect the stucco from any minor slips.
Affix the masonry bit to the drill, then drill a hole that is at least the depth of your concrete screw.
Affix the screwdriver bit into the drill. Drive the concrete screw into the hole until only 1/2 inch of the screw protrudes from the wall.
Peel off the masking tape and clear away any dust. Then hang the picture on the screw.