Very cool. Reminds me of the guy I met working at the post office (in Clifton, NJ) a few years back who mentioned during a brief convo that he had shot many of the big bands at MSG and many other smaller venues back in the 1970's, including Queen. He said they were all on slides and I offered to have copies made of whatever he had. I gave him my number but I never heard from him. I should take a drive to that post office, again.
But yes, that sort of picture is great. There was a great Queen book out a few years ago (a big one, can't remember the name) that had loads of unofficial pictures like this. Really furthered by understanding of the band.