A woman has been detained accused of damaging a masterpiece by the French romantic artist Eugene Delacroix, at a branch of the Louvre in the town of Lens. The 1830 painting titled 'Liberty Leading The People', celebrates the French uprising, the July Revolution of 1830. It is known as one of the inspirations for the Statue of Liberty, a gift from France to America.

The incident took place on Thursday and the 28 year old woman who was described as 'unstable', was held after being caught scrawling a graffiti tag on the monumental picture. The vandal told told police she had scrawled "AE911'' with an indelible marker on the painting, to draw attention to an organisation that appears to believe the 9/11 attacks were a conspiracy.

The museum in the northern town of Lens said the work could easily be cleaned but would be examined by a restorer. The Louvre Lens museum only opened in the former mining town in December. The painting by Eugene Delacroix, which featured on the pre-euro, 100-franc French banknote was being exhibited in Lens for a year.

The mark may be "easily cleaned" but a restoration expert was being sent from the parent museum in Paris, the museum said in a statement. No decision has yet been taken on whether the painting will have to be removed, the museum was quoted as saying by French broadcaster France 3. The local prosecutor, Philippe Peyroux, said that he had requested a psychiatric examination of the vandal. He added that the woman, whose identity has not been released, had a "French-sounding name".

Eugene Delacroix was the leading exponent of Romanticism in French painting. He was trained by the Neo-classical painter Pierre Guérin, from 1816 to about 1823. Guérin also taught Géricault. Delacroix first exhibited at the Salon in 1822. In style his work shows the influence of painters he had studied, notably Rubens. He was an admirer of English painting, and visited England in 1825. In 1832 he travelled to Spain, Morocco and Algiers. After the Revolution of 1830 he was favoured by Louis-Philippe, and later by Napoleon III, with a long series of official commissions, beginning in 1833 with a series of decorations in the Palais Bourbon.