That is a tough one :). Fluxus is a 'created' movement, with its 'meaning' essentially defined by the artists who join, each of them defining it his own way.
In contrast Pointilism is easy. Just look at the painting up close and if it is a lot of individual dots of color then it is a pointilist painting ;-))
So the best answer I can give is to say that that is a Fluxus photo because the guy who took it says it is.
Here is your other example:
