The term was in use in advertising by the early 20th century. Many gyms and fitness studios use the word "silhouette" either in their name or in their advertising. Historians of costume also use the term when describing the effect achieved by the clothes of different periods, so that they might describe and compare the silhouette of the 1860s with that of the other decades of the 19th century. A desirable silhouette could be influenced by many factors. The invention of crinoline steel influenced the silhouette of women in the 1850s and 60s. The posture of the Princess Alexandra influenced the silhouette of English women in the Edwardian period. See advertisement left. Because silhouettes give a very clear image, they are often used in any field where the speedy identification of an object is necessary. Silhouettes have many practical applications. They are used for traffic signs (see pic below). They are used to identify towns or countries with silhouettes of monuments or maps. They are used to identify natural objects such as trees, insects and dinosaurs. They are used in forensic science. For interviews, some individuals choose to be videotaped in silhouette to mask their facial features and protect their anonymity, typically accompanied by a dubbed voice. This is done when the individuals may be endangered if it is known they were interviewed. Computer vision researchers have been able to build computational models for perception that are capable of generating and reconstructing 3D shapes from single or multi-view depth maps or silhouettes  Silhouettes of ships, planes, tanks, and other military vehicles are used by soldiers and sailors for learning to identify different craft.