1. An system for detecting an object of interest in a scene, comprising: one or more processors and a memory, the memory having executable instructions encoded thereon, such that upon execution of the instructions, the one or more processors perform operations of: receiving an image frame of a scene; extracting features from the image frame, the features being descriptors, wherein the features are extracted from the image frame by performing operations of: creating three threads, one for each of three independent scales; providing, for each thread, a link to the image frame and a set of running parameters; running each thread, in parallel, to identify descriptors in each of the three threads; upon completion of the three threads, compiling the results from each of the three threads into a full set of dense Scale Invariant Feature Transform (SIFT) descriptors (DSIFT); quantizing the DSIFT descriptors to generate a pyramid histogram of visual word (PHOW) features; implementing a sliding window protocol to slide a window over the image and analyze PHOW features that fall inside the window; and determining if the PHOW features represent the object of interest and, if so, then designating the window as a location in the image with a detected object of interest.