I used Photoshop, simple gradients on each edge to fade it to the color the forum uses, bascially creating what you call a feathered photo.
Then when it came to things I didn't want faded, like speakers, I used a mask to hide the fading layer to bring them back.
Some of the more complicated ones with stronger fades I used a path tool to precut areas of the image and place them on top, like a lot of the wire kit. Then a little more work to fade some areas like trasparent plastics to look clear so it doesn't pop out against the white background.
So it was all done manually, no automatic feature, but usually you can do one thing in Photoshop many many different ways. I now notice some edges on some of the images that I need to fix so they blend into the forum better.
I'm a graphic artist so I'm in photoshop all day. Here's an example of a more intense job I did at work with many cuts and fades. Illustrator was also used for this too:
http://premium1.uploadit.org/TimothyB/graphic_starwars_tree2.jpg