Teaching assistant Sheila Sillery-Walsh from Birmingham took the photo on her iPhone 5c when she visited the former prison in April while on holiday in San Francisco with her partner, Paul Rice.
The 48-year-old said: “Alcatraz Penitentiary is a must-see for any tourist. However as soon as we entered the prison, everything felt very eerie. I didn’t feel comfortable there.
“Whilst doing an audio-tour of the place, I casually stopped to take a snap of the empty visitation block window on my iPhone.”
The couple have tried to find out the identity of the ghostly woman in the photo by contacting staff at the Alcatraz site, but none of the old-timers could recognize the woman in the picture.
“I am so curious to know who she could be though – perhaps she was a female visitor of a prisoner who kept returning back. I would love to know why she’s shown herself in my photo.
“Weirdly when we were near that cell, a woman came on the audio tour who used to visit a prisoner. It makes you wonder.”