1. A computer-implemented method of identifying a contour for an object depicted in an image, the method comprising: determining, by one or more computing devices, a contour direction for a point on a source contour for the object; determining, by the one or more computing devices, a plurality of rays extending from the point on the source contour based at least in part on the contour direction; constructing, by the one or more computing devices, a graph model based at least in part on the plurality of rays; and constructing, by the one or more computing devices, a contour based at least in part on a path through the graph model; wherein the contour is constructed notwithstanding one or more occlusions of the object depicted in the image; wherein constructing, by the one or more computing devices, a graph model based at least in part on the plurality of rays comprises: constructing, by the one or more computing devices, a plurality of nodes of the graph model, each of the plurality of nodes representing one of the plurality of rays; and constructing, by the one or more computing devices, a plurality of edges interconnecting the nodes in the graph model, each of the plurality of edges representing an intersection between the plurality of rays; and wherein constructing, by the one or more computing devices, the graph model comprises determining, by the one or more computing devices, an edge weight for each of the plurality of edges in the graph model based at least in part on an area between the rays associated with the nodes interconnected by the edge and the source contour.