As far as we concern, those pictures can be used by anyone. However, most of those pictures are not in the public domain and are under copyright protection of their respective owner. Permission to use those pictures must be granted by the copyrightholder at any given time (we have been given permission by them). So in reality you will have to contact the copyrightholder to ask permission.
Hello, I'm also curious about photo usage. I currently work for the Stafford Air & Space Museum here in Weatherford Oklahoma. We are wanting to use some photo's from your website for non profit, educational purposes. I noticed a few images specifically the tail fin images with different countries flags on them, have a copyright for this site. I am curious on how to submit a permissions letter for use of the photos if any is needed. Thanks