Looking into this, the first thing that came up was a technology that used infrared light to determine the curvature of the pages of a book so it could be scanned non-destructively (in normal scanning, the pages need to be flat - before google's idea this was only possible with glass plates, which was inefficient, or dis-binding the book, which destroyed the book). This was patented with [patent 7508978][1]. A nice, concise explanation of this is available [here][2]. A diagram of this is shown below: [![google book scanner][3]][3] Now, for the x-ray, don't have to open the book scanner. As far as I can tell, this sounds a whole lot like multispectral imaging (more about this [here][4]). I couldn't find any references to google doing this, but it can be done using infrared light. This technology was used to read ancient documents where it appeared to be black ink on black paper, but infrared was able to distinguish (more about this [here][5]). This has also been used on paintings. Another technology I found that uses x-rays was used to examine scraps of paper inside medieval bindings without taking off the binding (more about that [here][6]). This is called macro x-ray fluorescence spectrometry. More information about this is available [here][7]. I'll be updating this as I find more information. Hope this helps! ------------------------------------------------ **Edit**: I just today found [another site][8] about this that looks very promising. MIT has created a scanning system that can analyze the letters of nine pages. There is a video on the page that explains this in great detail. [1]: http://www.google.com/patents/US7508978 [2]: http://www.cnet.com/news/patent-reveals-googles-book-scanning-advantage/ [3]: https://i.sstatic.net/RjQTg.jpg [4]: https://en.m.wikipedia.org/wiki/Multispectral_image [5]: http://www.washingtonpost.com/wp-dyn/content/article/2005/05/29/AR2005052900811.html [6]: https://www.theguardian.com/books/2016/jun/04/x-rays-reveal-medieval-manuscripts [7]: https://en.m.wikipedia.org/wiki/X-ray_fluorescence [8]: http://news.mit.edu/2016/computational-imaging-method-reads-closed-books-0909