does anyone know how they did this ?

[Laszlo Kovacs]

Well, I think it depends on the source.
Is is a screenshot form a video, or just a single photo?
If it’s a video, then you should turn to the pros at the After Effects forum, because this is probably Trapcode’s 3D Stroke.
I don’t know of such plugin under Photoshop, but if was a photo, and I had to achieve this, I’d surely use 3D Stroke (it’s possible to import layered Photoshop files into AE). I’d then mask out the actors where I want the strokes to appear behind them, apply the effect, and export a single frame back to Photoshop.
Done.
Or, simply brushes in Photoshop? I’m not sure…

HTH

Laszlo
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Life is too short to drink poor wine.

[Phil Radelat]

Someone “traced” the individuals with a flashlite with an open shutter on the camera with a very small F-stop (notice the large depth-of-field). Then they fired off a fill-in flash at a desired exposure.

Obviously some tests were performed to find the right amount of time/F to expose the light coming in through the sides. Usually it takes a few tries to get the flashlight traces where you want them, but with today’s digital cameras that doesn’t take too long. I’ve done stuff like this.