How do I get this fashion portrait effect?

You write too much (for me) for such a very simple concept...

Moving dark object reduces exposure time of lighter background... Creates "dark smear" effect.

Cannot be done if the EV of the lighter background greatly exceeds the white point of the film/sensor.

That's it - Simple, easy to do in-camera with controlled lighting, and so not worth paragraphs of witter

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Simon
http://www.simonstanmore.com
http://www.simonstanmorestuff.info