Mr. Kelley and his longtime collaborator, Stanley Mouse, combined sinuous Art Nouveau lettering and outré images plucked from sources near and far to create the visual equivalent of an acid trip. A 19th-century engraving from “The Rubaiyat of Omar Khayyam†inspired a famous poster for a Grateful Dead concert at the Avalon Ballroom in 1966 that showed a skeleton wearing a garland of roses on its skull and holding a wreath of roses on its left arm.