Standard toy-store jigsaw puzzles obey certain rules that make the problem more tractable that it would otherwise be.
Standard rules include: (1) the puzzle has a rectangular outside border; (2) pieces form an overall rectangular grid so that each interior piece has four primary neighbors (left, right, above and below); and (3) pieces interlock with their primary neighbors by tabs, consisting of an “indent” on one piece mating with an “outdent” on its neighbor.
Another rule is optional: (4) each piece has no neighbors except its primary neighbors, that is, the cutting lines between pieces meet only at +-junctions rather
than a mix of +-, T- and Y-junctions. Our algorithm can solve reasonably big apictorial jigsaw puzzles (100 or more pieces), even if they do not obey rule (4).