Tracker based AR is the one which requires a tracking image to be used as a reference on which the digital content will be displayed. A tracker image can be anything, as long as it has enough unique visual points. This types of AR experiences are supported by almost all the mobile devices with a single/double high resolution camera.
In a marker/tracker based AR, when it is published then the user needs to put up physical printed copies of the tracker image branded with vision code. Any customer when scans vision code through mobile application will be able to view the digital content over the tracker image.