AN unfinished self-portrait of a York-born artist is expected to fetch up to $30,000 - about £20,000 - when it is auctioned by Sotheby's in New York.

The picture is of William Doughty, born in York in 1757 - but who painted it was initially in dispute.

Sotheby's had said it was by Doughty's teacher and friend Sir Joshua Reynolds (1723-1792), one of the 18th century's most dominant artists.

In the auction catalogue for its sale on Thursday, January 25, the portrait is described by Sotheby's as "an interesting and unique work in Reynolds's oeuvre".

However, an expert on Reynolds, Professor David Mannings, believes the work is a self-portrait.

Professor Mannings, of Aberdeen University, said: "I would seriously doubt that it is by Reynolds, and would say it is almost certainly a self-portrait by Doughty himself.

"Reynolds had many assistants and only painted one of them - his very first pupil. He didn't paint his later pupils."

The picture has no signature on it and no markings that reveal its origin.

But after being contacted by the Evening Press, Sotheby's of New York confirmed that the picture was a self-portrait, one of only a few works painted by Doughty before his untimely death at the age of 25.

Doughty's portrait of the Rev William Mason, his mentor, which hangs in York City Art Gallery, is considered to be amongst his finest works. Only a few other examples of Doughty's work, which can be identified, exist.

Professor Mannings believes that Doughty so closely imitated the style of Reynolds that the work of the two artists can easily be confused.

Professor Mannings said: "None of Reynolds's pupils looked more closely at his master's work and managed to imitate it more successfully."

After Sotheby's spoke to the Evening Press and Professor Mannings about the painting's origin the auctioneers changed their opinion about who painted it.

Chris Apostle, head of the Old Masters Collection at Sotheby's, New York, said: "We are going to change the attribute, but not the estimate of the price we expect. We are going to goldcard the picture when it is auctioned, which means we are now going to make a very special feature of its history."

Doughty's untimely death may explain something of the vibrancy of the portrait.

Mr Apostle said: "It is very immediate and fresh. It has these touches where the artist cleaned his brush on the side of the canvas, thinking he would finish the picture later."

However, Doughty's early promise was cut short when he died in Lisbon, en route to India.

Mr Apostle said: "It is a truly beautiful picture, and I will be very sad when it is sold and no longer in my office.

"What would be great, though, would be if it went back to Yorkshire."