Regular contributer John Short submitted the following photoshopping post on adding smoke to an image (click to enlarge example images).
Thought you might like a new imaging technique to make smoke.
1. The first job is to set the foreground and background colors to white and mid grey
2. Duplicate the layer, draw the shape of the smoke area with the lasso tool with a feather of 15 and fill the shape with clouds ( filter,render,clouds )
3. Now we need to add some motion blur ( filter,motion blur ), set the angle to match whichever way your smoke is moving and the distance to suit the movement you want to create.
4. Now use the shear tool ( filter, distort,shear ) to move the smoke as you would like it to appear
5. Then select ( filter,liquify. ) Using the warp tool move the smoke to give light and shade as needed
6. Now you can deselect the lasso. With a large eraser brush set to an opacity of no more than 6% ( I used 4% ) blend the smoke from the edges to the middle creating the final shape. You should also adjust the layer opacity to blend the complete effect with the master image.