Below is a fine collection of double exposure photography examples from the portfolio of Dan Mountford all of which have been created within the camera. Photoshop was used to alter the colors and to add various vector shapes, for example; in the image below.
Anybody can create double exposure photography, but the choice of what to combine together can make or break the piece. Dan Mountford's created a body of work that illustrates a great example of what good choices look like, evidence of this lies within the fact that his images have become what I would consider viral on both Béhance and Flickr. Racking up near total of 1,000,000 views, and of course, they look fantastic!