"The right way to frame the question, I think, is whether an artist who creatively appropriates a ... photograph needs to pay for a license to do so. This strikes me as a hard question. [Doug] Lichtman’s take is that there was a well-functioning market here, so that all Fairey would have had to do is ask for permission to use the photo (and perhaps pay a small fee) in order to avoid liability concerns. And Garcia has said that he would have given Fairey permission to use the photo if Fairey had simply asked him about it beforehand .... If that were true, it would be a strong argument against fair use ...."
He goes on to discuss the question whether the fourth factor "should include the enormous positive impact that Fairey’s taking has had on Garcia’s career (his photography is much more in demand now that he is associated with the iconic Obama poster)." The AP's lawyer calls this the "I did you a favor by ripping off your work" claim, but Fagundes finds it convincing: "at the very least, it seems to me that this argument should be part of the factor-four discussion rather than dismissed as readily as it is by most courts and commentators." In the end, he concludes that "the fair use issue is a truly difficult one."
Marquette's Bruce Boyden, who's been doing his own muti-part series on the case, turns up in the comments to say, in response to Fagundes's point that it may in fact be true that "Garcia is much better off thanks to Fairey’s unauthorized use than he would have been in a world where that use never happened":
"That's one possible world; but here's another one: The world in which everything is the same as it is now, except that Fairey paid Garcia a license fee before making the poster. Garcia is clearly worse off in the actual world than he is in that possible world, to the tune of X hundred dollars (whatever the license fee would have been), and his right to make the decision. ... You could argue that if Garcia had sought a fee, Fairey would have gone elsewhere; but that runs into the point that ... if any old photo of Obama would have done, Fairey could have gotten one for free from the campaign. There's reason to believe here that not just any old photo would have sufficed."
Finally, I refer again to the recent Catcher in the Rye decision, where Judge Batts (who also has the Cariou-Prince case) said that the fourth factor "requires the courts to 'consider not only the extent of market harm caused by the particular actions of the alleged infringer, but also whether unrestricted and widespread conduct of the sort engaged in by the defendant ... would result in a substantially adverse impact on the potential market for the original.'" The defendants' argued that that there was "no evidence that 60 Years will undermine the market for Catcher or any authorized sequel," but Judge Batts countered that "it is quite likely that the publishing of 60 Years and similar widespread works could substantially harm the market for a Catcher sequel or other derivative works."
UPDATE: This update is relevant here too.
UPDATE 2: Doug Lichtman adds a comment (just below Boyden's): "Imagine, for instance, that you made a movie based on my book. Would your movie likely increase sales of my book, and its sequel? Sure. Is that a windfall that indicates I should just pipe down and be grateful for your appropriation of my work? Hardly."