An unknown self-portrait of Vincent van Gogh has been detected under cardboard and glue on the back of another painting.

Art conservators at the National Galleries of Scotland said the image was revealed by an X-ray taken when they were examining the other painting in preparation for an exhibition.

Experts said Van Gogh often reused canvases to save money. The self-portrait is obscured on the back of Head of a Peasant Woman, from the 1880s.

It may be possible to uncover the hidden self-portrait, but the process of removing the glue and cardboard will require delicate conservation work.

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