ARToolKit markers are flat physical objects that can be tracked by the ARToolKit software.
Markers can be easily created in a graphics package and printed out, or even created by hand (such as using adhesive-backed felt).
The marker should conform to the dimensions shown here:
In order to track markers accurately, ARToolKit needs to know some details about each marker, including its width, and a description of the pattern within its frame. The width can be obtained by simply measuring the physical size of the marker.
Each marker is identified by the pattern within its frame. ARToolKit loads this information from a pattern file, which can be generated using the utility mkpatt, which comes with ARToolKit. The following screen shot shows pattern training with mkpatt.