1. A method of performing, by an image processing device, object detection in an image comprising: performing one or more tests of a test sequence for detecting a first object, on pixel values of a plurality of at least partially overlapping sub-regions of a first search window; generating a cumulative score based on results of said one or more tests on said plurality of sub-regions; comparing said cumulative score with a threshold value; and based on said comparison, selectively performing one or more of said tests of said test sequence on at least one further sub-region of said first search window, said at least one further sub-region at least partially overlapping each of said plurality of sub-regions.