Hi @inmoov
Sorry again for the delay in response. Your fiducial detection looks correct, thanks for posting that.
It seems like there is an inconsistency in the code, as @johnnyv noticed, fiducial_follow is actually configured for an odd fiducal size by default. The fact that your marker is the proper 14cm makes the robot think that it is much closer to the marker than it really is, causing it to back up. I have filed an issue for this inconsistency.
As a temporary fix, you can pass in the fiducial size manually roslaunch magni_demos fiducial_follow.launch fiducial_len:=0.14
Once you do that, you can put Magni up on blocks and move the marker around in front of it. When the marker is around 0.6 meters away and centered in the view, the wheels should slow down or stop.
Rohan