What is the ghostly hand resting on this girl’s shoulder in 1900 Belfast photo?

The spooky photograph above was taken in 1900 in Belfast, Northern Ireland and shows a group of linen mill girls in their work clothes, toolsets tied about their waists. One girl, pictured in the second row, far right, appears stand-offish from the others. Identified as Ellen Donnelly, her granddaughter explained:

“I don’t really believe in ghosts – but there have been a few odd going-ons around this photo!”

So, what is so unusual about the photo? Look at the girl’s right shoulder. There’s an unidentifiable disembodied ghostly hand gripping her shoulder!

The family had long wondered about the freakish hand resting on the girl’s shoulder. Experts have said the photo is untouched but have been unable to identify the clearly visible hand-like thing resting on her shoulder. It doesn’t look like a trick of light nor a ruffle on the shirt or another person’s hand.  As of now, the surreal hand in the photo remains unexplained.