Splicing together scanned sections of artwork

From: billpruitt.com


I put(using move tool) all 4 of my scanned sections(all same dpi,etc.) into a larger new blank image. I then moved each section into place, overlapping so it all lined up like one big picture. Only now the seams are still very evident. Each section was scanned at same parallel so no rotating was necessary. At this point, is there any way to get rid of the seams or blend them together? Any help on this frustrating matter would be greatly appreciated. Thank you.