Just a brief comment about djvu text layer, using IA files to digging deeper the topic.
FineReader OCR stores an incredibly detailed information in a proprietary format; then, various FineReader versions export something of this extremely rich set of information into different outputs - one of them being djvu text layer. It's worth to note that even if any information stored into djvu text layer can be extracted and used, the set of information wrapped into djvu text layer (both in lisp-like format or in xml format) is only a minor subset of original OCR information.
If someone is interested to get much more information, it can find it into abbyy.xml output; and Internet Archive gives it as abbyy.gz into the list of exportable files. It's a very heavy and complex xml structure but it is possible to parse it, end to extract from it any information wrapped into djvu text layer and much more - most interestingly, wortPenalty, that is, word by word, the resume of degree of incertainty of OCR recognition of the whole word.
We (I and Aarti) are digging into this mess, with fast preliminary results; you can see into [[it:w:Utente:Alex brollo/Sandbox]] some brief pieces of text extracted from abbyy.gx, where doubtful words (in the opinion of OCR software) are red. They can be easily managed by VisualEditor - caming simply from a simple span tag.