W. T. Freeman and E. H. Adelson, The design and use of steerable filters, IEEE Trans. on Pattern Analysis and Machine Intelligence, vol. 13, no. 9, pp. 891 – 906, September, 1991. MIT Vision and Modeling Group TR 126.
You can also see a prtical example of the use of steerable filter for classifying protein crystallography images and an example of a multi-resolution (in terms of 2D spatial frequency) steerable pyramid image that I made of Marilyn Monroe using the same original image that Andy Warhol used for his popart paintings.
This app has now been modified to work with HTML5 video instead of flash, much better!