We are faced with an issue of convenience versus freedom when we talk about licensing images. Because we are a nonprofit charitable organization with an educational mission, we can easily get non-free licenses to use images. Because we are a nonprofit charitable organization with an educational mission, we can make heavy use of the doctrine of "fair use" in the US.
But should we?
One of the things that our reliance on these alternatives does is work to undermine our broader mission, by reducing the incentive for the creation of free alternatives. It's more work to get those free alternatives, but the result will be worthwhile, I think.
We can set aside most of the licensing and legal issues, because I think we're fine there. Clause 7 of the license permits us to combine independent works, even proprietary works, and this clearly includes aggregating images and articles stored on the same server. For fair use, the license isn't implicated or violated in any way.
So I think resting our rejection of licensed and most fair use images on that argument is mistaken. I don't think that argument is valid, but more importantly, I think that argument is too hyper-technical and legalistic, implicitly assuming that it's o.k. for us to do it if the license says it is o.k.
The moral argument is the one that matters. Should we make use of materials that are available only to us because of our special circumstances, or should we follow a purist GNU philosophy?
I think we all know what Richard Stallman would say, and I for one will agree with him completely. The Wikimedia Foundation should be a beacon of what is possible with copyright freedom, and we should not allow anyone to ever point at our work and say "Yeah, they talk the big talk about free licensing, but what would their site be without all those proprietary licensed images and fair use exceptions?"
If that means less images for now, then it means less images for now. It also means that we have a very strong incentive to develop free alternatives.
--Jimbo