Pictorial representation of the concept behind Loopy Belief Propagation for Stereo Matching. The symbols in the central cell refer to sum-product Belief Propagation, one of the earliest and mostly widely discussed forms of Belief Propagation. Each cell sends a new message to its neighbouring cells at each iteration after in turn having received and processed new messages from the neighbours in the previous iteration. The outgoing message to a given neighbour is computed from the information received from the other neighbours previously, represented here by the three thin and one fat arrow.
Both formats are the same image, they are both included for your convenience, and because figshare apparently doesn't render .eps files in-browser but .eps seems to be the required vector graphics format for many publications.