MIT researchers are designing an imaging system that can read closed books. They tested the prototype on a stack of papers, each with a single letter printed on it, and the system was able to correctly identify the letters on the top nine sheets. The MIT researchers developed the algorithms that acquire images from individual sheets in stacks of paper, and researchers from Georgia Tech developed the algorithm that interprets the often distorted or incomplete images as individual letters. The system could be used to analyze any materials organized in thin layers, such as coatings on machine parts or pharmaceuticals. In the researchers’ setup, a standard terahertz camera emits ultrashort bursts of radiation, and the camera’s built-in sensor detects their reflections. From the reflections’ time of arrival, the MIT researchers’ algorithm can gauge the distance to the individual pages of the book.