Simplest shape detection with orientation

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Hi,

What is the simplest shape I can easily detect (least CPU intensive) on a Raspberry PI3 with a 170 wide angle lens? It will actually be a sticker attached to a moving object so I can control what the sticker is going to be The sticker can be tilted on both X and Y axis up to 50 degrees Distance from the camera will be between 1cm and 15cm and I am capturing only 320x240 to have a high FPS The output should be a set of coordinate like X,Y of the center of mass (I figured I can use moments for that) and orientation angle between 0-360 or -180 to 180

Thank you!