A bunch of the distorting effects in Photo Booth--Bulge, Dent, Twirl, Squeeze, and Light Tunnel can be customized. Once you select them, you can click the mouse in the picture and move it around to change the location of the distortion effect. For some of the effects, most notably Light Tunnel, this can make a big difference in the quality of the picture that you get in Photo Booth when using distortion effects.