Now where have I seen this image before?

It's probably one of the most common questions people ask when browsing auctions; "now where have I seen that painting before". Usually, either the auction house answers it for you, or the painting is rather obscure. But sometimes (though all too often), a copy after a well-known painting or work by a well-known master is given without any indication of it being a copy, which is annoying.

Hampel, from Germany, sells on 30 March 2017 a "Dutch school, 18th century" portrait of the mathematician and his wife, estimated at 900 to 1,200 Euro.

It is a run-of-the-mill copy of a Rembrandt, which is rather essential information. It is housed in the Royal Collection in the UK, and depicts not a mathematician but the shipbuilder Jan Rijcksen and his wife.