How do I detect squares/rectangle or an other shape with EMGU CV?

Question

I want to make an apps detect an square/rectangle in my webcam using EMGU CV (an OPENCV wrapper). The square/rectangle will have a solid color.

if it's posible I would like to obtain the width and heigth of the square/rectangle

In this video you can see what I would like to do.
http://www.youtube.com/watch?v=ytvO2dijZ7A&NR=1

I'm working with C#

Answer 1

If you already know the color of the desired object then you can segment the image based on that color. (Which may be why the rectangle disapears when the guy movies the direction to and away from the camera [differences in lighting]. Once you have the object segmented out of the image you can do region calculations on the image. [In matlab think regionprops]

Once you have the blob you can attempt to do model fitting to get a good approximation of the object being represented.