The offer of a Gottfried Lindauer painting stolen from a Parnell gallery for sale on the dark web has been exposed as a scam but police maintain it and a sister artwork will turn up one day.

Lindauer's Chieftainess Ngatai-Raure and Chief Ngatai-Raure, painted 134 year ago and together estimated to be worth up to $900,000, were stolen in a ram-raid on April 1 last year.

Six months later a listing appeared on the "White Shadow" market, a dark web auction site, claiming to offer one of the works for sale.

The listing was brought to wide attention by technology magazine Wired which reported the seller "Diabolo" promising to ship the painting, Chief Ngatai-Raure, anywhere in the world.

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A description in part read: "Here you can bid on a TOP SECRET original painting from Bohemian painter Gottfried Lindauer that was stolen in New Zealand, Auckland 2017."

The bitcoin auction appeared to attract several bids, the highest converting to $400,000.

But the officer in charge of Operation Bower, Detective Inspector Scott Beard, said inquiries strongly indicated the listing was a scam.

"The FBI were contacted and came to the conclusion that the site was likely a fake.

"I understand White Shadow is offline and has been down since November 24, 2017," Beard said.

"Diabolo" was not located.

Beard said it was common for people to create fake adverts or posts on dark net sites.

He said that conclusion was supported by art data site Artnome which claims to have tracked how the image purported to be the stolen painting was faked.

Using image-matching tools, Artnome's Jason Bailey identified how the image in the listing was photoshopped from two images.

The image of the painting came from photos in the media about the theft and the frame - and background wall - was sourced from a photo of another Lindauer painting.

The height of the painting was reduced so it would fit into the photo of the frame.

Once Bailey corrected the size a photo-matching tool showed a 99.9 per cent match between the source photo and the photo on the auction site.

Police, meanwhile, are optimistic the paintings will turn up. Beard's hunch is that the paintings are still in the country and may be used as a bargaining chip with police.

There was nothing to suggest long term planning. "The paintings were only put in the gallery's window that night."

CCTV footage shows three people, their identities masked by hats and scarves, involved in the 3.45am raid.

The framed paintings were snatched after a stolen Ford Courier ute reversed through the front window of the International Art Centre on Parnell Rd. That vehicle was left with its engine running half inside the gallery while the offenders fled in a white Holden Commodore.

"We looked at all Holdens of that colour and make that had been stolen, and while there is at least one outstanding, we have never located it."

Beard thought it likely the thieves realised the significance and value of the paintings only after media coverage.

Interpol, which has a works of art division, was promptly notified and a political motive was considered because of the subject of the paintings and because that was the motive behind the 1999 theft of a $2 million Colin McCahon painting.

It is almost 18 months since the Lindauers were snatched.

"Are the paintings gone forever? I'd never say that," said Beard.

"It's a bit of a cliche but like all unsolved investigations, loyalties change. Someone who was once a friend may not be now.

"The file is in the office. It's waiting for a lead. I never say never because all it takes is one phone call and it's game on again."

Art historian Dr Ngarino Ellis, a founder of the New Zealand Art Crime Trust, said history shows an array of motives for artwork thefts. Money from a sale or ransom was common. There were examples of them being used to barter in drugs or arms deals as well as thefts motivated by a vendetta.

Sometimes, "someone just likes the work and wants it on their wall".

That's how it was for a French waiter found with a collection of stolen art in his home including the work of grand masters, Ellis said.

In another bizarre example, a painting by abstract expressionist Willem de Kooning turned up 32 years after it was stolen, following the deaths of an elderly couple.

Women-Ochre, valued at US$400,000 when it was snatched and US$160 million when found, was in the main bedroom of Jerry and Rita Alter's home in Cliff, New Mexico, a town of 293 souls.

Jerry died in 2012. Rita's death last year led to the discovery of the painting in a position where it could only be seen from inside the bedroom, according to news reports.

Neighbours and relatives were incredulous. They described the Alters, both aged 81 when they died, as "lovely", "nice" and also "quiet". He had worked as musician and teacher, she as a speech therapist.

Last month the Arizona Republic reported that a relative and executor of the pair's estate had chanced upon a snapshot while sorting through family albums that may help solve the mystery.

It shows the Alters enjoying Thanksgiving dinner with family in Tucson, Arizona, the day before the painting was taken from Tucson's University of Arizona Museum of Art.

Gallery officials believed the thieves - a man and a woman - distracted a guard, cut the painting from its frame and hid it under a coat.

The FBI, which is investigating, has made no comment but the Washington Post reported circumstantial evidence tied the Alters to the heist. The couple owned a red sports car similar to the one used by the thieves and photos show Rita wearing a red coat like the one worn by the female thief.

And there is this. A short fictional story published by Jerry in the year before his death tells about the theft by an older woman and her granddaughter of a famed emerald from a museum.

The pair escape a suspicious guard and leave behind no clues. The emerald safely stashed in a private room, the fictional characters triumphantly conclude, "And two pairs of eyes, exclusively, are there to see!"

Notable New Zealand art thefts

Urewera Mural

by Colin McCahon. A work spanning three large panels, stolen in 1997 from the Āniwaniwa Visitor Centre, Lake Waikaremoana, returned 15 months later with Tūhoe identity Tame Iti and arts patron Jenny Gibbs acting as negotiators.

Still on Top

, by James Tissot, stolen in 1999 by lifelong crook Anthony Ricardo Sannd. He demanded a half a million dollar ransom for the return of the painting which was found rolled up under his bed eight days after the robbery. The painting was restored and returned to the Auckland Art Gallery.

Pania of the Reef, a 60kg bronze statue stolen from Napier's waterfront in 2005, recovered from a garden shed eight days later and returned to its spot.