Watermark location via back-lighting and recto removal

We consider the problem of locating a watermark in pages of archaic documents that have been both scanned and back-lit: the problem is of interest to codicologists in identifying and tracking paper materials. Commonly, documents of interest are worn or damaged, and all information is victim to very unfavourable signal-to-noise ratios - this is especially true of 'hidden' data such as watermarks and chain lines. We present an approach to recto removal, followed by highlighting of such 'hidden' data. The result is still of very low signal quality, and we also present a statistical approach to locate watermarks from a known lexicon of fragments. Results are presented from a comprehensively scanned nineteenth century copy of the Qur'an. The approach has lent itself to immediate exploitation in improving known watermarks, and distinguishing between twin copies.