Image caption A known portrait of Rembrandt (L) with the newly uncovered painting (R)

An unfinished self-portrait by the Dutch master Rembrandt has been discovered under another painting using advanced scientific techniques.

No detail is visible in the face, but experts say it matches a reproduction from 1633 that has an inscription saying it is by Rembrandt.

X-ray scanning was used to detect the pigments in hidden layers of paint.

A leading expert on Rembrandt said he was convinced of its authenticity based on similarities in painting style.

The unfinished self-portrait was discovered under another panel said to be by the master - Old Man with a Beard.

Image caption The self-portrait is hidden under this image of an old man, attributed to Rembrandt

Art historian Ernst van de Wetering, head of the Rembrandt Research Project, said there were key technical similarities in painting style between the self-portrait and authenticated works by Rembrandt that date to the 1630s.

There is also a copy of the painting that must have been made by one of the pupils in the artist's studio.

The self-portrait was revealed when the painting was scanned at the Brookhaven National Laboratory in New York and the ESRF light source in Grenoble, France.

Koen Janssens of the University of Antwerp, Belgium, told BBC News: "The portrait is considered to be an early work. So this documents a little bit better how Rembrandt in his early period was functioning in his workshop.

Prof Janssens, who led the X-ray scanning, added: "Which projects did he start? Which ones did he finish? How many are there that he changed his mind about and started over."

The technique of X-ray Fluorescence Spectrometry allowed the different chemical elements present in the paint to be mapped, revealing different views of the hidden image.