Blur the Background - A Photoshop Introduction - The Digital Photography Weblog:

I've come across this one more than once - you take the photo of the moment, then when you're in post-processing, you realise that a bit of blurring on the background would make the subject really stand out. Most often for me, this happens with an impromptu portrait, and a background that's just too busy, too active to stay in the background. Something that has Details that detract from the subject of the photo, details that you want to blur into obscurity.

You want to introduce depth of field after the fact.

This little tutorial shows you how.

Technorati Tags: photography, photoshop, portrait