http://bit.ly/2bZiL0H ‎ "Terahertz frequency profiles distinguish between ink and blank‎ paper."

Scanning an unopened book with a camera that emits ultra short bursts of radiation allows one to 'read' it's contents.‎ This application is particularly useful for researchers like those who reference books at the Metropolitan Museum in NY who want to read books that are so rare or fragile that curators are hesitant to allow the books to be touched.

Soon the developers will have enhanced this technology ‎to scan more than 9 pages and one day, whole books will be 'read' this way.

There is a nice vid in the article too.

ScrnGrbCred: mit.edu