The band have used a classic painting by French Romantic painter Eugène Delacroix from 1830 called ‘Liberty Leading The People’ (La Liberté guidant le people). It depicts the a woman personifying Liberty in the French Revolution leading the army in their march over dead bodies holding the French tricolour flag aloft. It’s currently on display in The Louvre in Paris.
Coldplay aren’t the first band to use the image on an album cover. In 1999 Japanese rock outfit Dragon Ash parodied the cover on the sleeve to their album ‘Viva La Revolution.’