Id like an explanation for how the blue background light in this photo is somehow "overlaying" the model's hair and the back of the chair. How could this effect be setup and reproduced?
Probably, the effect might be achieved with the help of slow sync flash method (a combination of slow shutter speed and firing flash). Not much lighting involved other than the on-camera flash.
As the subject is crisp when the flash is fired and the blur caused with the long shutter speed. The reflections on the lips confirm that the flash is fired.
Reproduction: Being more accurate the effect might have used rear curtain Sync. In this the model might have moved slightly front after the shutter is pressed (probably with chair, as overlays are on chair also) and then flash that is fired at the end of the capture would have frozen the subject sharply. This effect can be reproduced on an moving subject, with motion effect by the same time freezing the subject.
A lot more images can be found here: http://www.flickr.com/groups/slowsynch/pool/
It's a long exposure plus flash.
The clue is that the only blurring is coming from the window light. The subject is heavily backlit, without the flash they would be a silhouette. The flash momentarily illuminates the subject, and because that area would be black otherwise no light from the subject is recorded during the period that the camera is moving hence there is no motion blur at alp on the subject.
It doesn't matter whether it was first or second curtain flash as the subject was stationary you don't have the problem of motion blur being in front of the subject.
This technique could be reproduced by using a long exposure and a zoom lens.
With an exposure of say, 2 seconds, right after the shutter is pressed, quickly zoom out by a few millimeters and keep the lens at that second for the duration of the shot.
The blurred images looks like a motion blur moving toward the model. Quickly zooming out would create this blurred "overlay," with the model in focus once the zoom has settled.
It does look like slow sync, although I'm not 100% convinced, given the static subject. You could reproduce that in post processing by duplicating the layer, giving it a heavy blur (50px or more) and then roughly masking back in the in-focus parts of the image.