tl;dr: Decorrelation stretch, a NASA JPL technique originally developed to enhance satellite imagery by mapping colors to an expanded range, has been repurposed via Jon Harman's Dstretch plug-in (built on ImageJ) to reveal faded ancient rock art invisible to the naked eye. It has uncovered hundreds of previously unseen paintings at sites like Angkor Wat, Norway's Årsand 1, and Egypt's Beni Hassan, and has expanded into other uses including aerial archaeological surveys in Greece and imaging tattoos on mummified remains.