1. A method to determine skew in an image of a scene in real world, the method comprising: computing a plurality of values of an indicator of skew in a plurality of regions in the image; wherein each region in the plurality of regions comprises a plurality of pixels that are contiguous with one another and the region comprises a local extrema of intensity in the image; determining whether skew of the image is unacceptable, by applying a predetermined test to the plurality of values of the indicator; and requesting user input to correct skew of the image, in response to skew being found to be unacceptable by the determining; wherein one or more of the computing, the determining, and the requesting are performed by at least one processor coupled to a memory.