1. A method for defining a boundary separating a first region and a second region of a digital image, the digital image including one or more color arrangements characteristic of the first region and one or more color arrangements characteristic of the second region, the method comprising: determining using a learning machine, based on one or more of the color arrangements, which pixels of the image satisfy criteria for classification as associated with the first region; determining using a learning machine, based on one or more of the color arrangements, which pixels of the image satisfy criteria for classification as associated with the second region; identifying pixels of the image that are determined not to satisfy the criteria for classification as being associated either with the first region or the second region; and decontaminating the identified pixels to define a boundary between the first and second regions.