The nanoCam, full name nanoCamera, is very small. Likewise, it is used to observe things closely. For example, during the testing for entrance into the Institute. Golds would be stripped and examined by Coppers from the Quality Control Board. The like of biometric nanocams can be installed on a ring. Presumably this is how students of the Institute of War were observed. It was also how people knew of Darrow killing Karnus, as Fitchner recorded it.