To create double exposed portrait images, there are a few steps you need to take. The first step is of course taking your photos. Once you get three photos, (One being a portrait picture and the other two being your other pictures) you need to open up all of your images and adjust the exposure to a way that you feel looks right. Then, you need to dodge the image. Use the dodge tool photoshop has provided and outline our portrait picture with it. After outlining it, fill in everything except the portrait you outlined with the dodge tool. After dodging the portrait picture, it's time to drop in your first image. Let's say for the sake of me telling you the steps, it's a picture of a tree. So after you drop in the picture of the tree, Click the blend mode drop-down menu at the top of the layers panel and choose "Screen" to blend the trees with the portrait. Then your hit command/control+T to enter the free transform mode. Once you're in there, use the bounding box to rotate and resize the layer to find an angle that you think is well put and covers all of the portrait. Once you do this, hit enter to apply it. Next, you need to tone the image. To do this, you click the Create New Adjustment Layer icon in the Layers panel and choose Gradient Map. Then you go in the Properties Panel, click the gradient preview drop-down menu, then click the cog icon and choose Photographic Toning. Once you're in there, adjust the options to create a mode that suits your image. After you get everything done, your image should look amazing and nicely blended together.
You would want to make these images to bring out some symbolism in you. Maybe you would want to show your interests in a creative way. Or maybe you just want to experiment in photoshop on what you can do. Whether you're doing something symbolic or just for fun, you should definitely try out double exposed portraiture.
