1. A computer-implemented drag-and-drop pasting method of seamless image composition, the method comprising: receiving, by one or more computing devices configured to facilitate seamless image composition, a region of a first image, the region including a visual object to be pasted into a second image; and calculating, by the one or more computing devices, a boundary for pasting such that visual seams are minimized, wherein the calculating of the boundary further comprises iteratively determining a minimal color difference between a plurality of pixels in each path of a plurality of paths via performing a shortest closed path calculation, wherein performing the shortest closed path calculation comprises: determining a band of pixels between a user-selected border of the region of the first image and a border of the visual object; determining a shortest linear distance between a point on the user-selected border of the region of the first image and a point on the border of the visual object; applying a transverse cut to the band of pixels along the determined shortest linear distance; using the shortest closed path calculation, calculating at least one path of the plurality of paths associated with a minimum cost around the band from at least one pixel of the plurality of pixels along one side of the transverse cut to an adjacent pixel on the other side of the transverse cut; and selecting the at least one path associated with the minimum cost as the boundary, wherein the minimum cost is determined based on a least color variation along the at least one path of the plurality of paths.