1. A method comprising: acquiring data of a digital image which depicts one or more objects; determining a first size of a first detection window and an initial location of the first detection window in the digital image; wherein the first detection window encompasses a first portion of the digital image; determining, for the first detection window, first detection window data that represents the first detection window at a first image resolution level; determining a first set of face detection tests that are to be applied to the first detection window data; applying the first set of face detection tests to the first detection window data to determine a first confidence level value that indicates a likelihood that a particular object, of the one or more objects, is included in the first detection window; in response to determining that the first confidence level value is not greater than a first threshold value: determining a second size that is greater than the first size; determining a second detection window that has the second size; wherein the second detection window encompasses a second portion of the digital image; determining, for the second detection window, second detection window data that represents the second detection window at a second image resolution level; determining a second set of face detection tests that are to be applied to the second detection window data; and applying the second set of face detection tests to the second detection window data to determine a second confidence level value that indicates a likelihood that the particular object, of the one or more objects, is included in the second detection window; and wherein the method is performed using one or more computing devices.