This past week I've been playing around with some more variations on double exposures. This on is an image of a model I just photographed and two shots of a city for an urban background, plus some an image of smoke to give it atmosphere. I've had the photograph up on my computer for several days and keep tweaking it. I'm still not sure it's finished. I'll see how I feel about it in a couple more days.
Photoshop layers provides the vehicle for pre-visualizing multiple exposures. The layers can be treated in a number of different, see-through ways. It's a matter of playing with them and shuffling the images until it looks right.
For this image the woman layer was on top and its mode changed to "lighten". The urban background layer was placed on the bottom as a "normal" layer, but has been treated to a "photographic toning" "gradient adjustment". A second close-up urban shot of a building grid facade on top of this had its mode changed to "overlay". On top of that is an image of smoke against a black background with its mode changed to "screen", which makes the blacks disappear leaving only the white smoke.