A very simple Android application using OpenCV for image recognition

I have a card with a matrix of colored squares. The card has 4 reference points at 4 corners and each of these colored squares are at some known distance/coordinates from these reference points. A user will take a picture of this card through their phone camera. I need an app to do the following: 1. Detect these 4 reference points, get their coordinates in the same, and find the distance (in pixels) between their centers. Using this pixel distance and actual distance (in mm), find the number of pixels per mm. 2. Using this value, navigate to the center of each of the colored squares (which are at known coordinates from the reference points coordinates) and extract the average color value in a small radius around that point.