Tracking and Augmenting Business Cards using Studierstube Tracker
Markers is usually expected to be surrounded by black borders and containing a black and white pattern or image. Naturally the marker's border can be made very thin (down to zero) if the image inside the marker is rather dark. Even more the marker content does not have to be black and white or grayscale since the tracker converts to grayscale internally anyways.
The image on the right shows an example business card that can be tracked robustly.
The following video shows tracking of a business card using an unmodified version of Studierstube Tracker, configured to use a non-square marker with a very thin border (if the border is actually set to 0.0 white color tends to spill into the unwarped area thereby decreasing the detection quality). The video was recorded on an unmodified Asus P552W mobile phone running Studierstube ES.