Hi guys! I'm doing a simple game project for university. The tricky part is the input: The game has to be controlled via WebCam (the player is waving around a blue postcard in front of the cam). Now here's the problem: How can I find the position and rotation of the postcard from the captured image? I already post-processed the image a little to make it Black and white. Take a look at the pictures below: First one shows the post processed image (256x256), the second one what I would like to have (the four corners). So for the human eye it's very easy to find the rectangle in this picture...but for my PC? I actually don't have the slightest clue how to approach this... Can you help me out?

wikipedia on edge detection might be a good starting point