These photos are apparently of a Palestinian using some sort of homemade grenade launcher. It looks like it could be a 40mm grenade in the barrel, or maybe some type of 40mm less/non-lethal grenade like round, such as tear gas.

It appears to work by striking the firing pin (a drill bit) with a stone. I would not want to be within 200 yards of somebody firing that weapon.

Russian VOG-25 40mm Grenade. Photo from gunbroker.

UPDATE: DrStrangegun noticed that the size of the launcher is very simular to Russian GP-30 launcher. The Grenade is propelled through the vents you see in the above photo. Much like a rocket.

GP-30. From Wikipedia.

Hat Tip: MP.net