All explained by Mr Windley at Clavius. If in doubt, give Clavius a clout.
The wikipedia image has been modified too. Other than being far darker, the image has been rotated, the bottom cropped and "sky" added to the top, and the fiducials have all been removed.
It must be fun to lead a life completely unburdened by reality. -- JayUtah
"On two occasions, I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able to rightly apprehend the kind of confusion of ideas that could provoke such a question." -- Charles Babbage (1791-1871)
What causes the ground near Aldrin to be brighter in this picture?
Is it a remnant of opposition effect, or is it light reflected from the suit or LM? Or is the ground actually different there?
The Apollo 11 LM drifted a bit to the left just before touchdown. Thus the terrain immediately around and behind Aldrin was somewhat scoured smoother and more free of very fine dust, leaving both a smoother surface and a somewhat higher percentage of glass beads in the lunar regolith exposed to sunlight. Since the sun was behind and to the right of Aldrin, the result is that the ground now reflects light better towards the down-sun direction where Armstrong with the camera was standing.
You might want to check out my analysis of photo AS11-40-5903 on my web site. Here is the link. Just scroll down to the photo.