It is definitely within his right to sue. He performed his part of the contract, at least in part, they failed to perform theirs at all, he has the right to sue for performance. He spent time taking the photos, and has the right to be compensated for that time.
Whether or not it is the right thing to do morally or economically however, is a different story.
But having the right to something, isn't an argument for or motive to do something. It just means that it is an option.
The question I asked whas the motives to recommend that he takes it to court.
To motivate a specific action is to show what advantages there are, and show that it is likely that the advantages are bigger than the disadvantages. What is the cost, and what is the probability of a net gain (money, goodwill, freedom to control own time, ...)