12. A system comprising: a memory; a computing device; and a processor programmed to: sense depth data for a plurality of frames that include hand movement; for the plurality of frames, process the depth data, wherein processing the depth data comprises: segmenting the depth data to isolate a hand represented in the plurality of frames; determine that a principal direction of the hand is not pointing in a predefined direction in an image plane; based on the determining, rotate the hand such that the palm of the hand is substantially parallel to the image plane and such that the principal direction of the hand is pointing toward the predefined direction in the image plane; perform normalization on the rotated hand to provide normalized hand data to compensate for scale and relative hand size of the hand; and extract feature values corresponding to the normalized hand data; and recognize the hand movement as a hand gesture based upon the feature values provided to a classifier.
12. A system comprising: a memory; a computing device; and a processor programmed to: sense depth data for a plurality of frames that include hand movement; for the plurality of frames, process the depth data, wherein processing the depth data comprises: segmenting the depth data to isolate a hand represented in the plurality of frames; determine that a principal direction of the hand is not pointing in a predefined direction in an image plane; based on the determining, rotate the hand such that the palm of the hand is substantially parallel to the image plane and such that the principal direction of the hand is pointing toward the predefined direction in the image plane; perform normalization on the rotated hand to provide normalized hand data to compensate for scale and relative hand size of the hand; and extract feature values corresponding to the normalized hand data; and recognize the hand movement as a hand gesture based upon the feature values provided to a classifier. 16. The system of claim 12 , wherein processing the depth data further comprises detecting the hand by: determining a plurality of hypothesized hand regions; and determining a hand region from among the hypothesized hand regions based upon processing one or more previous frames of depth data.