At Steve Zarelli Space Authentication, I review thousands of autographed astronaut photos every year. Also, as a collector for over 15 years, I have seen many, many more.
So what is the most valuable and desirable single signed astronaut photo? Most people would probably assume it is a photo signed by Neil Armstrong. Armstrong unpersonalized white space suit portrait photos with a strong signature can fetch $5,000+. In a RR Auction Space Auction last fall, this Neil Armstrong signed photo closed at $14,350.
All that said, I will submit that the most valuable single signed astronaut photo is an unpersonalized white space suit photo signed by an astronaut many generalist collectors may not have heard of before - Jim Irwin.
Jim Irwin was the 8th man to walk on the moon with Apollo 15. He was a good signer prior to his untimely death in 1991. He signed many, many items and Irwin signatures can be had for as little as $30 - $50 on postal covers, cards, etc.
So, why would he be the most valuable single signed astronaut photo? He hated his NASA white space suit portrait and didn't like signing it. If you sent him one, he would send another signed photo instead. I estimate I see 100 Neil Armstrong signed white space suit portraits for every one Irwin signed white space suit portrait. They are that rare. A handful come to market a year, and even less unpersonalized. Irwin frequently personalized, so unpersonalized examples are exceedingly rare.
And what makes this so valuable is many space collectors try to collect the "set" of white space suit portraits. So you have many collectors competing for an extremely rare signed item, even if an Irwin signature itself is very common.
Perhaps the finest Jim Irwin signed white space suit photo in existence is currently featured in the RR Auction Fall Space Auction. Not only is it signed perfectly, it boasts an exceptional inscription, "Apollo 15 LMP, 8th moon walker, the chance of a lifetime."
As I write this, bidding is up to $7,560 with over 5 days to go. I would not be shocked to see this break $12,000.
Interestingly, after I reviewed and approved this item and the auction preview went online, noted collector and dealer Ken Havekotte wrote on CollectSpace that he obtained this directly from Irwin when Irwin visited his Merritt Island, FL, home in July 1987. Havekotte went on to write he sold it many years ago, so apparently he is not the current consignor.
Zarelli Space Authentication