OpenGL coordinates tranformation

  
if (marker.numDetected>0 && marker.numDetected<10){  
		marker.getMatrix(7, m);  
		glMatrixMode( GL_MODELVIEW );  
		  
		glLoadMatrixf( m );  
		cvRect(0,50,20,20);  
		glPushMatrix();  
		glEnable(GL_DEPTH_TEST);  
		ofBackground(255, 255, 255);  
		botao.draw(0,50,20,20);  
		cvSetImageROI(grayDiff.getCvImage(),cvRect(0,50,20,20);  
		buttonImg.scaleIntoMe(grayDiff);  
		countBlackPixels();  
		squirrelModel.draw();  
		  
		glPopMatrix();  
	}  
  

As you can see in this bit of code i’m getting the transformation matrix from the AR marker and i’m drawing a button with the same orientation. What i want to do now is to extract the pixels of the original image where the button is being drawn, so that i can evaluate whether somebody is “clicking” on it or not.
I thought this way the cvRect would also be altered by the matrix. But no, i keep on cropping the same rectangle over and over. How can i acess the coordinates of the image after the matrix transformation?

Regards