1. A computerized method comprising: computing a blur difference between a first and a second image of a three-dimensional scene, the first image acquired through a camera lens focused at a first picture number and the second image acquired through the camera lens focused at a second picture number, wherein the first and second picture numbers represent different focus distances of the camera lens; and predicting a third picture number based on the computer blur difference, wherein the third picture number is subsequently used to auto-focus the camera lens on the scene.