How was this background image created?

[paulk7737514]

The 3 cars were obviously isolated and outer glow was applied after the 3 were combined in a single image, but the outer glow is not consistently the same amount around the image.

http://www.teesautos.com/graphics/bg_header.png

[melissapiccone]

Perhaps they made a duplicate layer of the 3 cars, turned it all black and applied a gaussian blur... lots of ways they could have made it.