The document scanner has long been a tool of the most usual appearance and scanning a digital copy of a document is now of such ease that anybody can do it. Nevertheless, there is a large gap between a pro scan of a full book and the slightly better than average Xerox-like copy that we all do.
Most of it comes from the use of masterful algorithms of cleaning, cropping, re-cropping, aligniment, correction, optimisation that are usually included in some very complex and very expensive pro software scanning tools. Thanks to Scan Tailor, this is no longer the cas. It is open source and it does it all like the pros.