If you wind up with an unsigned painting, there are a few ways to ID the artist. Trace its provenance, for instance, and consult the experts. But what if the experts disagree?

In the late '80s, Toronto art dealer David Mitchell acquired a painting believed to be that of Tom Thomson. It was a two-sided sketch featuring landscapes of Algonquin Park, and he bought it off of two Vermont sisters whose mother, they said, bought it in the '20s. Many experts, including A.J. Casson, the last surviving member of the Group of Seven, viewed the sketch and declared it a Thomson. Just as many, though, thought otherwise — trouble for the dealer who staked $80,000 and his reputation on the piece.

Today, the painting belongs to a private collector, who bought it as a genuine Thomson. On Dec. 5, 1989, though, CBC News jumped on this unsolved mystery — one of many surrounding Canada's most famous artist, whose paintings, just this past week, earned new record prices at auction.

Group of Seven forgeries are not without precedent, but this piece, often referred to as Spring Landscape with Snow/Northern Mist, was the first Thomson to undergo scientific analysis. The Canadian Conservation Institute scanned the painting with infrared cameras, hoping to suss out evidence of fraud. As CBC News put it, "high tech tackles a high-brow problem." But science alone wasn't enough to solve this mystery. Watch the full report.