The photograph was taken against a white background so our images could easily be extracted and digitally superimposed onto the cave picture.
I don't know why they chose a white background.
I do know that my hair is white, so when they did the masking to remove my image from the white background, it took a slice off the top of my head, too.
If I ever go back, I'm wearing a white shirt and standing side-on so it removes my belly.