This photograph, titled "Stones back of alter at Stonehenge" as indicated on the back was in the collection of and licensed for use by Culver Pictures of New York. I was pleased to find Culver Picture is still in business and the nice lady currently in charge of keeping track of licensing at Culver confirmed that in 2005, this photo along with a number of other items from the collection were sold to a broker for eventual sale into the collectables market. In the end it turns out this was in fact the same fine seller I was dealing with on eBay.
Based on the optical illusion I will call the shadow stack, it looks like there is a stone leaning on #56 in this picture. It has been suggested that this was not the case, and it was shadows playing tricks on me. After examining the photo at greater magnification and levels of enhancements, it became apparent that the horizontal grain of the one stone was eclipsed by the more vertical grain of the more upright of the stones, and that was a trick of the eye that connected the contrast points to make it look to be resting on top. I have added a closeup that better showing the "grain lines".
In either case with a little help of the computer, this fine old photograph has cleaned up nicely. No matter what the date turns out to be, it is by far the oldest photograph showing a visitor at Stonehenge in the gallery.