Not sure about KLM, but NWA is very good about letting people take pics. As long as you're not bugging the captain durring flight, you'll almost for sure be allowed to take some cockpit pictures and here a good flight story or two
As far as window pictures, no one has ever come up to me and told me to stop, I've been able to get some decent takeoff and landing pics with NWA.
Seeing as KLM and NWA are pretty much the same airline, I wouldn't worry much about them either.
And thats my 2¢