That made the rounds on the internet a few months ago. I think the consensus was that while clever, the idea is kind of pointless. He *did* use it for guerilla marketing; well, guerilla propaganda at least.
First off, he relies on the pre-flash that most point-and-shoots use. This means he'll only be affecting, basically, tourists and such. Secondly, free speech and everything, but this guy is kind of a jerk. It's debatable whether his political messages are accurate (as opposed to grossly exaggerated), and it's also debatable whether his audience -- hapless tourists -- really is appropriate. Sure, you can ruin someone's vaccation photos, maybe to a site closely liked to that vaccationer's heritage, family, etc. Why use some high-minded political message? Why not just admit you're a tool who likes screwing with innocent vaccationers?