A screen reader is a form of assistive technology (AT) that renders text and image content as speech or braille output. Screen readers are essential to blind people, and are also useful to people who are visually impaired, illiterate or learning-disabled. Screen readers are software applications that attempt to convey what people with normal eyesight see on a display to their users via non-visual means, like text-to-speech, earcons, or a braille device. They do this by applying a wide variety of techniques that include, for example, interacting with dedicated accessibility APIs, using various operating system features, and employing hooking techniques.