WHICH - Detecting different kind of Markers in OpenCV 2.x

I would like to have a good tutorial for finding different Markers.

Like square Markers with more information in it and without. How to warp it ect.
Round Markers and threesided Markers. I will add some images soon.
Would be nice if somebody has some freetime...

i know that the first steps are something like threshold and blur. find contours or keypoints/corners.
I am right now working on finding round Markers like which look like pizza - but its not that easy to find them in my picture - so there is some personal interesst in this tut.