Comment Don't (Score 1) 64
Just use images with a proper license and a company that is willing to license to you under terms that are not so fuzzy. CC sucks because it is so unspecific and creative types just don't understand the ramifications and limits of their choices. The sad thing is that the world would be a better place if CC never came into existence, because then you would at least have had a chance for proper public licenses to evolve.
Otherwise, you are a company, so you could probably just open up a sixpack of lawyers if you ever get into problems.
As for your stated problem, if you documented it for yourself that this was some specific license, then the courts can probably entice Flickr to just state what license was valid at the time.