Photoshop plug-in takes the pain out of extracting backgrounds

Fluid Mask 3 does an excellent job of isolating and cutting out objects that have high contrast or sharp edges from an image background. But the product really shines in difficult situations where foregrounds and backgrounds are similar, or where objects have soft, unfocused edges. Fluid Mask 3 analyzes an image and creates outlines at the edges of areas with distinct color and texture, breaking the image into regions that you can choose to keep or to delete. It also blends image edges to avoid artificial-looking, hard-edged cut-outs. The initial edge analysis occurs automatically and without noticeable delay.

http://www.macworld.com/article/60628/2007/10/fluidmask3.html