A hidden object game, also called hidden picture or hidden object puzzle adventure, is a subgenre of puzzle video games in which the player must find items from a list that are hidden within a scene. Hidden object games are a popular trend in casual gaming. Time-limited trial versions of these games are usually available for download, although many are free to download on app stores. They primarily make money through in-app purchases and ads. Popular themes include detective crime stories, adventure, gothic romance, and mystery.