Modern day forgers are able to replicate rare books printed using a mechanical printing press by using photopolymer plates, a process which involves taking a high resolution photograph of a page which was printed using a printing press and allowing computer software to create a three dimensional printed image of that photograph with depth for each letter present. This method produces pages which have an imprint mark as if pressed by a printing press but its fatal flaw is that it also provides depth to small lines around the margin of text which are picked up during the printing process. These lines should have no depth as they are merely extra ink which has been caught during the printing process but with photopolymer replicas, because the software used to extract three dimensional characters reads every single bit of ink as a marker to place depth, these lines appear to have depth within forgeries which is an immediate red flag in terms of authenticity as originals have no reason to possess depth. These incidental inking lines around the margin of the page are referred to as “shoulder inking”, and if they possess depth of any degree, it is a strong indication that the piece is a modern day forgery
