Can you tell which of those postcards has been designed by famous artists, sports stars and even the Prime Minister?
Postcard-sized artworks by Tracey Emin and David Hockney are among more than 500 being sold for as little as 99p at a secret charity auction.
The world-famous artists have contributed pieces along with hundreds of unknowns, including a four-year-old girl and a 100-year-old retired teacher.
A David Hockney original or a worthless amateur effort? It's a gamble...
Prime Minister David Cameron, comic Ronnie Corbett and former tennis star Greg Rusedski have also supplied their own mini-creations for the charitable cause.
Their works are being exhibited at the Towner art museum in Eastbourne, East Sussex. Without knowing who has created the works, people can bid for them on eBay until the auction, called The Big Art Secret, closes on Sunday.
Proceeds from the sale will go to St Wilfrid's Hospice.
Hockney's work is described as "an ink and colour crayon drawing on a postcard" and Emin has donated four postcards in her trademark style.
A rare glimpse into the psyche of David Cameron? Could be!
Kara Bishop, chief executive of St Wilfrid's Hospice, said: "This is an opportunity for anyone, not just art collectors, to support our charity and stand to gain substantially from it, be it in terms of owning a valuable artwork or from the enjoyment we can all get from a piece of art that truly strikes us as beautiful or moving.
"The auction will appeal to art collectors and complete newcomers to the art world but the beauty is, with artists spanning 96 years and from household names to hospice patients, nobody will really know which ones are by a famous artist until after the virtual gavel falls."
Matthew Rowe, artistic director at the Towner art museum, said: "The response not only from the art world but from all walks of life has been phenomenal.
"But the twist is in the secret - by obscuring the market value, who knows the true financial work of each postcard?"
Think you can tell the famous postcards from the amateur efforts? Take a look through then make your prediction below!
