1. A method of image labeling comprising; receiving at least one image and computing at least one global parameter of the image; and modifying an image labeling process according to the computed global parameter; wherein computing the global parameter comprises; selecting a subset of image elements in the image; for each selected image element determining a probability that the image element depicts an object having a specified global parameter; and combining the probability from a plurality of the selected image elements to compute an estimate of the global parameter.