I have an image the is larger than my screen and a mouse handler that selects the corners for a call to cvRectangle. If I select a corner near 0, 0 (top left) the start of cvRectange is at or near the correct position but the further I go to the bottom right, the more the second corner is off. It looks like a scaling issue between the image that is 1980x1080 and the screen that is 1366x768. How can I get the correct coordinates rom the image so that the call to cvRectange produces the correct rectange Ian