ARToolKit is a software library for building Augmented Reality (AR) applications. These are applications that involve the overlay of virtual imagery on the real world. For example, in the image to the right a three-dimensional virtual character appears standing on a real card. It can be seen by the user in the head set display they are wearing. When the user moves the card, the virtual character moves with it and appears attached to the real object.

One of the key difficulties in developing Augmented Reality applications is the problem of tracking the users viewpoint. In order to know from what viewpoint to draw the virtual imagery, the application needs to know where the user is looking in the real world.
ARToolKit uses computer vision algorithms to solve this problem. The ARToolKit video tracking libraries calculate the real camera position and orientation relative to physical markers in real time. This enables the easy development of a wide range of Augmented Reality applications. Some of the features of ARToolKit include:

-Single camera position/orientation tracking.
-Tracking code that uses simple black squares.
-The ability to use any square marker patterns.
-Easy camera calibration code.
-Fast enough for real time AR applications.
-SGI IRIX, Linux, MacOS and Windows OS distributions.
-Distributed with complete source code.