Methods and systems are described herein for high-speed observation and recognition of an object which is within or passes through a designated area using 3D image data and tomography, stereo-photogrammetry, range finding and/or structured illumination. Such a security system may comprise multiple pairs of 3D sensors surrounding the designated area such as a portal or doorway. Alternatively, it may comprise a 3D sensor which is capable of acquiring 3D image data of an object that is situated in front of it. Using at least one 3D sensor and a 3D data collection technique such as structured illumination and/or stereo-photogrammetry, 3D image data of the object is acquired. 3D image data representing the object's surface may be determined based on the acquired data and may be compared to data representing known objects to identify the object. Methods for fast processing of 3D data and recognition of objects are also described.