In the picture below I didn't like all the people that ended up in the shot. I found a digital solution by covering up the people by cloning more smoke.

I scanned the image above, cropped it and added some levels before calling up the layers palette via Window/Show layers or by using the shortcut key of F7.

I created a blank layer above the train by clicking the centre icon from the bottom of the layers palette. I then double clicked the Rubber Stamp Tool (clone tool) and selected sample merged by ticking the small box at the bottom left of the dialogue box. This allowed me to clone onto a separate layer so that any time I can make changes to what I have done. No permanent changes are being made at this stage to the base image.

I enlarged the area to be cloned and selected a fairly large soft edged brush. By holding down the alt key and left clicking the mouse I can sample an area of smoke. After that I can paint in extra smoke as I see fit.

TIP…. Alter the opacity of the clone tool from time to time to get a softer edge and to enable blends to look more natural. A degree of practice may be needed to get the feel of the clone tool.

All the time you are carrying out this work nothing is being transferred to your original image but onto a separate layer as shown below.

When you are satisfied with your work flatten the image via Layer/flatten image which will combine the separate layers to form one image. See below