Double exposure is a combination of two images where one image is overlaid onto another at less than full opacity for artistic intent. The technique yields very interesting results and allows the photographer to produce ghost images and mirror images. I like this technique as the images can tell a story and create deeper feelings.
This can be done in-camera or in post-processing. In film photography, double exposures are made by exposing the same portion of film twice, resulting in the second image being superimposed on the first.
In digital photography, double exposures can be made in-camera in some cases when it’s available as a creative effect in a body, in photoshop. Federico Bebber my inspiration for several projects uses the double exposure technique.