1. A method for fast three-dimensional imaging using defocusing and feature recognition in a fast three-dimensional imaging data processing system having a sensor and a processor, comprising: capturing a plurality of defocused images of an object on the sensor by receiving signals transmitted from the object through a plurality of off-axis apertures of a mask and through a lens, where the data processing system understands the type of object being imaged; using the data processing system to identify a priori known segments of interest in each of the plurality of defocused images with a feature recognition algorithm; and using the data processing system to match the identified a priori known segments of interest with three-dimensional coordinates according to the positions of the images of the segments on the sensor to produce an output image containing the three-dimensional position of each segment of interest.