Aruco is an paper marker tracker.

To use it print the sample AR marker image.

You may also generate a marker interactively, using a site made for that (remember to change the Dictionary option to "Original ArUco").

Wave it at the camera, making sure the roll value is close to zero. The model gets recognized no matter its roll value, and putting it upside down or 90 degrees to the side will swap/invert pitch and yaw, beware.

Following that, base it on cardboard, avoiding either glue bleeding through the paper, or tape covering the marker respectively, depending on the method used. Leave two or three centimerers of the empty paper around the markings.

Please keep in mind that marker has to be waved at the camera at a neutral pitch angle of at least 15-25 degrees -- since it's planar, solver gets confused when pose approaches identity. When mounting it on a hat, ensure a relatively oblique angle that keeps the raw pitch value positive at all times. Otherwise, sudden spikes in pitch value ensue.