1. A computer-implemented method for generating invisible junctions, the method comprising: receiving, with a processor, an electronic document; applying, with the processor, a distance transformation to the electronic document to generate a distance transform; detecting, with the processor, a skeleton in the distance transform; determining, with the processor, junction points in the skeleton as the invisible junctions, the junction points having a distance transformation value based on the distance transform; determining, with the processor, a junction size for at least one junction point, the junction size based at least in part on the distance transformation value; and creating, with the processor, a feature descriptor for each invisible junction, the feature descriptor including the junction size.