Motion without movement
The basic idea
1d crosssections of filters. (a) Even phase (G_2).
(b) Odd phase (H_2). (c) Filters modulated in phase.
Note the apparent rightward motion of the filter ripples.
Image of Einstein
(a) and (b): G_2 and H_2
filters were applied to an image of Einstein.
(c) Image phase modulated as above.
When viewed as a temporal
sequence, this generates the perception of rightward motion,
yet image remains stationary.
Steerable filters conveniently allow this illusiory motion effect to
occur in any direction, just by changing the orientation of the
quadrature pair of filters.
Reference

W. T. Freeman, E. H. Adelson, and D. J. Heeger, Motion without
movement, ACM Computer Graphics, vol. 25, no. 4, (SIGGRAPH '91), pp.
27  30, July, 1991.

B. Cabral and L. Leedom, Imaging vector fields using line integral
convolution, ACM Computer Graphics, vol. 27, no. 4, (SIGGRAPH '93), pp.
263  272, July, 1993.

D. Stalling and HC. Hege, Fast and recolution independent line
integral convolution, ACM Computer Graphics, vol. 29, no. 4, (SIGGRAPH '95), pp.
249  256, August, 1995.