He was the first man to walk on the Moon, but Neil Armstrong didn't have any good photos to prove it. He had the camera most of the time, so it was Aldrin who got all the awesome shots. Sure—he was on grainy TV and reflected on Buzz's visor but—except for his footprint—there were no cool shots of Neil.
This is why this image is so amazing and special. It was taken by the top camera of the Eagle, as Neil walked his first steps across the Sea of Tranquility. Only for a fraction of a second, with his mirror visor up, you can clearly see Neil's face as he walked by the Lunar Module, going to do his next mission task.
It's not only an awesome image. It's also a perfect summary of Armstrong's character too. For him, it was all about the mission and his country, never about himself. As his family and his biographers say, he was America's (greatest and) most reluctant hero.
The elusive frame was spotted in an old film reel by space author Andrew Chaikin, who included it in this book [Voices from the Moon]