1. In probe-based pattern matching, a method for placing a plurality of probes at selected points along a boundary in an image including a plurality of pixels, the method comprising: providing a computer programmed to perform the steps of: determining an arc position for each boundary point along a segment of the boundary, starting with zero at a first boundary point at a first end of the segment, and increasing while moving away from the first end by an amount equal to the distance between the boundary points along the segment; determining the total arc length of the segment as being the arc position of a boundary point most distal from the first boundary point of the segment; determining a probe spacing value along the segment; and determining a number of probes to be placed along the segment using the total arc length of the segment, and the probe spacing value.