A bit more on Copyright and to try to explain this situation.
In light of having 4 sources that report that Firaxis did not pursue permision for their works (of which at least 3 think they should had asked permision, the other being a stockphoto house gave a me sort "meh" answer, apparently they let these things slide).
Letting it slide is actually the way to go for these things. It's still likely unethical, but pursuing legal action is odd in these sort of cases.
Also
everyone is doing it.
From videogames we love like Arcanum:
That's no easter egg, that's Daniel Day Lewis
To other games we love like Victoria:
That image dating from 1907, so it's public domain... I think, it belongs to Ford, I'm not sure if they still pursue copyright for it.
To other games by Paradox:
The copyright is still there http://www.famouspictures.org/mag/index.php?title=Flag_on_the_Reichstag
And many more, did you know the first 2 Duke Nukem games stole graphics from Turrican as well as other games?, you know now:
http://www.nemmelheim.de/turrican/news/duke/
And here's more, it's not only the videogame industry, but the clothing industry, the design industry and advertising industry (boy they love stealing alright):
http://youthoughtwewouldntnotice.com/blog3/
And if you think that's bad, both Electronica and Rap had their humble beginnings by ripping off 6 brief seconds from a little known song by The Winstons, perhaps you've already have heard about it, if not here's a neat little documentary that explains it best:
http://www.youtube.com/watch?v=5SaFTm2bcac
Yes, that sample is even used in the PowerPuff Girls intro song, that's were you've heard it before, Powerpuff go!
No one pursued legal action for it, still not technically
legal though. Music now has some pretty strict regulations about sampling music (you have to pay for the rights now). But this is mostly because music companies have better lawyers and lobbyists. The Music industry pushes constantly for copyright protection so that no one downloads their music ilegally. But some of their finest have been caught stealing before. Among artists that have stolen, you even have staunch anti-download advocates, incluiding Metallica, who have also (allegedly) stolen around 3 songs themselves (making it legal to download those 3??).
http://www.cracked.com/article_18500_the-5-most-famous-musicians-who-are-thieving-bastards.html
And here lies my main beef with the whole copyright issue, the fact that Civilization V has to date one of the most sophisticated forms of copyright protection (Steam). In other words, you cannot copy what they have done, that would be ilegal, but they can copy from you if they wish. It's been over a month since this issue came up, yet there has been no signs of Firaxis caring much about this issue (but did you know Civ World is comming?!!). Photographers and other artists do not have multi million dollar companies backing them up.
We make the culture that we live in, mass forms of media such as the ones companies or politicians manage have a huge impact in our perception of morals and ethics. In a culture were it's alright not care a whole lot about forms of cheating, or even celebrating them, is it really that surprising to see the public disregarding corporate copyright claims?