The first challenge I am attempting is Challenge 3 - Play Spot-It(TM). There are actually quite a variety of the game available as seen on Amazon, but the version we are attempting is what looks to be the original version. Given any two cards, there is one image that can be found on both cards - although scale and rotation may be different.
I have posted my first attempt as a zip file for you to download and review the source code. The pipeline is: scale|gray|blur|Canny|contour(2px)|contour(1px) & blur|houghCircle.
I have also taken a few more sample images:
by JJ Stiff - jjstiff arroba hotmail punto com - 25 June 2014