Nice to see all your comments, thanks all. What I find fascinating about this photo is the status of the Picasso light drawing.
A lot of thinking about photography always suggest that it is different from drawing because it is not created by the conscious actions of the artist, and thus is more akin to taking an imprint of reality, like one would do with clay pressed upon a bas-relief. (Personnally, I don't agree with that position for a myriad of little reasons.)
I find that this picture dramatizes nicely the opposition between our common conceptions of drawing and photo by showing that one needs not accept the idea that a photo is necessarily a direct record of reality. Picasso's drawing does not exist elsewhere than on the negative his light pens inscribed.
I think if one sticks to the above conception of photography as record of direct experience, then this work is a composite, but I'm more incline not to see it as such, because none of the actions that went into its production differ from that in the ordinary taking of a photograph. I think it rather shows that the definition of a photography must be extended beyond this realistic hypothesis.