The good news: Finally the US National Association of REALTORS (NAR) is educating Realtors about copyright issues involved with listing photos (see this NAR article). This should have started long ago, but let's be thankful that they finally realized that photo copyright is an area that agents need education. This is a very significant development because agents in the US respect and pay attention to the NAR. Most real estate offices use NAR materials to help educate agents. The fact is, agents are probably going to pay more attention to information like this coming from the NAR than they are if it is coming from their professional real estate photographer! Notice that the article has three agreements for agents to download.
The bad news: Some local real estate offices are interpreting this copyright info to be a reason that agents should shoot their own listings. For example, here is an excerpt from an email that Jonathan, on the Big Island, got from one of his clients:
...The safest way to make sure that you're safe, of course, is to take your own photos. But if you must hire a photographer to take photos for you, please make sure that you have secured all the rights to use the images in writing...
So when explaining your license agreement to your agent clients it may be helpful and add credibility to your story to refer to this NAR article. Most US agents are NAR members so it should add to your credibility.
Update - More bad news: As you can see below in Joel Rothman's (an Intellectual Property Attorney) detailed and insightful comments you should not sign the NAR's license agreements. Joel says to NAR general counsel:
...Your sample agreements, and in particular the exclusive license, is overbroad and overreaching for the typical agent-photographer relationship. If NAR wants to perpetuate disputes with the photographers their members depend upon to earn their commissions, and continue to sow seeds of distrust, then these sample agreements will accomplish those goals. I will advise my photographer clients not to sign NAR’s sample agreements...
Thanks Joel for you valuable input! Note that we have a copy of Joel's recommended photo license agreement in our e-book: The Business of Real Estate Photography.