A woman who posted a selfie of her winning Melbourne Cup ticket - including its barcode - has been fleeced for her $825 winnings.

"Winner winner chicken dinner", read the caption on the photograph of an elated Chantelle holding her winning ticket.

The Perth woman - whose last name has been suppressed - backed the 100-to-1 shot Prince of Penzance and jockey Michelle Payne in Tuesday's Melbourne Cup.

But someone else dined out on her winnings after they used the barcode on the clearly displayed receipt to withdraw the cash from an automated machine.