1. A method for detecting properties of sample tubes, comprising steps of: a) capturing a series of images of a sample tray using at least one overhead camera; b) receiving at a processor the series of images of the tray from the at least one overhead camera; c) extracting, by the processor, a plurality of image patches from each image, each image patch corresponding to a portion of each image based on features in each image; d) automatically determining, using the processor, from a first subset of the plurality image patches, each patch corresponding to one of a plurality of slots in the tray, whether each of a plurality of slots contains a sample tube; e) for those plurality of slots that contain a sample tube, automatically determining, using the processor, from a second subset of the plurality image patches, each patch corresponding to the top of the sample tube, whether each sample tube has a cap; and f) for those tubes that do not have a cap, automatically determining, using the processor, from the second subset of the plurality image patches whether each sample tube has a tube-top cup or is a plain tube.