Hmmm, that's a very hard decision to make.
Not because I'm not sure if the right thing to do is to take pictures or save this guys life, but because I'm not sure how you would save somebody's life that has done something as drastic as that.
And if you saved somebody from a death like that, how much of the rest of their life is really going to be worth living?
I also have a problem because I believe that a person has the right to do what they want to their body, and if this person wants to die in such a tragic death, what right do I have to stop them? Now, if the person was doing this to somebody else, then there's no question, stop the crazy person, save the lives of the innocent.
I think the question as to should you help or not really doesn't have anything to do with taking pictures. It's a deeper moral question as to how you view life and respecting the wishes of those who choose to end theirs.