Detective Work Using Terahertz Radiation (image) Fraunhofer-Gesellschaft Caption The terahertz scanner not only finds hidden wall pictures, but can also prove the presence of biocides on pieces of art. Credit © HfbK Usage Restrictions The picture may be used for editorial purposes only. It is protected by copyright. The use is free of charge if the reference is mentioned. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.