I'm not sure that'd even be effective. It seems like you'd have a pretty strong case for fair use defense in the US as the use could be commentary/criticism or

I'm not sure that'd even be effective. It seems like you'd have a pretty strong case for fair use defense in the US as the use could be commentary/criticism or even as "education". There are no guarantees when it comes to fair use protections, but it'd certainly be hard to say that the photographer is losing money because people interested in his work are flocking to view protest signs or anti-abortion pamphlets.