Obviously a film library for studying.  These would be very highly classified films.

I am assuming that E. F. is Ellington Field, which would fit with the other photos I have in the group.  Ellington is currently a Joint Air Base and home to NASA flight operations for the Johnson Space Center.

On the front:

Photo 12

Official Photo US AAF Training Command EF Texas

and stamped on the back:

“Official Photo USAAF by AAF Training Command.”