Another image search engine (based on the appearance of the image).
The result of this process is 3 arrays (one for each color channel) holding the truncated, quantized wavelet coeffients, plus the average colors for each channel. This is the wavelet signature.
Using an metric devised by Finkelstein, et al., wavelet signatures can be compared. Basically, the algorithm is this: The more signature matches between two images, the closer the score of the two images.