17. The method of claim 16 wherein a feature vector for a given horizontal location in the potential keyword includes a representation of the topmost pixel at the given horizontal location having a value above a threshold, a representation of the bottommost pixel at the given horizontal location having a value above the threshold, and a representation of pixel values between the topmost pixel having a value above the threshold and the bottommost pixel having a value above the threshold.
17. The method of claim 16 wherein a feature vector for a given horizontal location in the potential keyword includes a representation of the topmost pixel at the given horizontal location having a value above a threshold, a representation of the bottommost pixel at the given horizontal location having a value above the threshold, and a representation of pixel values between the topmost pixel having a value above the threshold and the bottommost pixel having a value above the threshold. 19. The method of claim 17 wherein the representation of pixel values includes the number of pixel transitions through a threshold value.