Now, to fun things. I tried to make non-square marker qtrack mod based on this method. You can see in this video how far I could push it:
but, overall, this was a failure. Unlike that guy, I had only one shape to detect, so at 1st I thought I could use max ICF value between blob and marker contours (ideally 1) and compare it to confidence threshold. However, this picked way too much false positives. So in 2nd iteration, that you see in the video, I had to calculate max ICF values for few hundred blobs 1st, and then pick the blob with max of those values. This worked somewhat better, but in the long run, it is still unreliable. Here is a distribution of max max ICF values thresholded at 0.7:
As you see, even shape as simple as flash logo produces really poor values most of the time. Another equally significant problem is that BitmapData’s threshold() method produces poor contours when threshold is not optimal: over-illuminated patches of the marker punch random “holes” in its binarized version and contaminate detected contour. To sum up, you will have to stick with quad markers for some time, sorry.