Detail from 'Unknown Landscape'. The mound could be natural, an unusual structure, or even a coal waste-tip. See full painting below.
A landscape painted by the famous Potteries artist Reginald Haggar is mystifying experts.
The picture is being donated to the Staffordshire Hoard appeal, and will be auctioned in early December.
Its owner Pam Mallalieu said: "I very much hope that the answer to the 'mystery of the mounds' in the picture will be unearthed now."
Reginald Haggar, who died in 1988, was a well-known artist, teacher, ceramic designer and historian.
The sale of the painting is being handled by the Friends of the Potteries Museums & Art Gallery. It shows a rugged landscape, with rocks, trees and shrubs - with a mysterious, mound-like structure in the background.
The chair of the Potteries Museums Friends, Isabelle Killicoat, said she hoped that the scene would be recognised by someone: "We would like to know what this strange building is, and where it was painted."
Although many pieces by Haggar are owned by the Potteries Museum, experts there say they are baffled as to the site of the view in the painting.
Haggar spent the rest of his life in north Staffordshire after moving to the area in his twenties. He was happy to be known as a Potteries artist and much of his art depicted local scenes.
Pam Mallalieu, who is a former manager of the Potteries Museum, said an identification of the scene might add value to the painting, which would then in turn benefit the Staffordshire Hoard appeal.
The Hoard consists of more than 3000 gold pieces dating back to Anglo-Saxon times. It was discovered buried in a field near Tamworth in summer 2009.
Although more than £3m was raised to pay for the Staffordshire Hoard treasure, which is to be housed in the West Midlands, more than £1m is still needed to pay for conservation and research costs.
Anyone who recognises the scene is asked to
email the Friends
or contact the Potteries Museum & Art Gallery on 01782 232323.
The full painting shows the vantage point of the artist, perhaps suggesting it's a countryside view
The painting is to be sold at the Louis Taylor Auction House in Hanley on Tuesday, 7 December.