I developed a small application for the iPhone (for academic purposes) that allows the user to take a picture of an object. At the time the picture is taken, the accelerometer data from the phone is also recorded. The user will shoot from top to bottom (bird view) of the image, that is, the phone should reasonably be at an angle of 90 degrees to the object. However, it cannot be guaranteed that the angle will always be 90 degrees.

Given that I have accelerometer data (x, y, z values) when the image is taken, I believe that there is a way to build a transformation matrix to transform the image as if it was taken at a 90-degree angle, However, I'm not quite sure how to build this matrix.

As I mentioned, this is for academic games, so as soon as I capture the image data and x, y, z, I just send it to one of my computers for further processing. Processing is done using Python and OpenCV.

Any help or pointers would be greatly appreciated.