Art fakes and mistakes at the National Gallery

A forgery purporting to be a 15th century portrait of the family of Federigo Montelfeltro, Duke of Urbino, aims to capture the style of works such as Pedro Berruguete's painting of the duke and his son Photograph: The National Gallery

Portrait of Federico da Montefeltro, Duke of Urbino, and his son Guidobaldo, (1477) attributed to Pedro Berruguete, as the previous painting imitated Photograph: The National Gallery

An Old Man in an Armchair by a follower of Rembrandt, (17th century). The portrait was bought by the National Gallery in 1957 under the conviction that it was the real thing. The museum's experts since determined it to have been painted by one of the artist's pupils or followers Photograph: The National Gallery

The Sunset by Giorgione (1506-10). There is no doubt. says the gallery, that this work is by the Venetian master, Giorgione. But, large parts of it are reconstructions painted by another hand – in particular the St George and the dragon and the island towards the right of the work Photograph: The National Gallery

The Virgin and Child with Two Angels (c1470-80) by the workshop of Andrea del Verrocchio. This is another work not solely painted by the assumed artist but by at least two says the National gallery, as there is a stark difference in the quality of painting of the angel on the left, to the infant at the bottom Photograph: The National Gallery