Blending two or more images into one
Whenever you are working with 2 or more images that you want to be combined into a single one, you are composing, because compositing in Photoshop means to combine 2 or more images to make a single image, and in this post you will find a basic guide, some concepts, and a few fundamentals topics before starting any compositing project.
A convincing composition has to be visually consistent, but before you begin using Photoshop you must find 2 or more images that shares the same (or very similar) angle, light direction and perspective. Although you can change all of those things in Photoshop, having images that shares similar caracteristiques will save you a lot of time.
Your best friend when compositing in Photoshop are the Layers. As the most challenging part of the composition are the details, having your images into different layers will help you to visualize better the final result while you start masking (not deleting) parts of that layer to blend it with the next one by making parts of this layer transparent. If you set up each element as a different layer you will find that compositing will be much more easier because you will be able to move, rotate, scale, match colors, etc. of each element around the canvas until you are satisfied with the result.
There are many ways to make parts of an image transparent, but you should forget the eraser tool. When you are making a composition in Photoshop think on Masks. Masks allows you to go back and forward without compromising any previous work you may have made into an image element, correct any mistakes that you have made, and improve the details of your selection.
The Blending Modes feature of Photoshop are a great ally to compositions. You will probably don´t use most of them, but the Overlay and Soft Light blending modes will be present at some point. Using some (or both) of these 2 modes you can add some color, contrast and light to your image element, and as the layers where you will be applying these modes will be at the top, it will help you to bring the whole image together because these modes takes care of lighter and darker areas of the image at the same time.
Sometimes blending modes are not enough to make a part of an image transparent in such a way that it perfectly blends with another layer and you need to be more precise to hide the areas that you do not want to appear. Although Photoshop have some selection tools right in the Tools Panel, those are not all and you may need some of them depending on your image. Selections, besides being made manually, can be made by edge detection, by color and tones and by channels.
A Manual selection can be made using the Marquee or Lasso Tool, they are simple and effective, but you can also use the Pen Tool and convert it to a selection, which will be more precise and you can edit it at any time by saving the path.
The edge detection method is a bit more advanced in terms of complexity because they work based on the content edges, this method is useful to start and make a rough selection, of course, similar tools like the Quick Selection or Magnetic Lasso Tools are also a good option.
But if the areas that you want to select are visible plainly (like a sky for example) you may think to use the Magic Wand Tool, but there is a better way to make it by using the Color Range selection or even the image channels.
Remember that to make a good composition in Photoshop it is not only a matter of using the right tools, layer modes and choosing the proper images, you also have to consider some design elements and principles as well to end with an unbeatable result. If you want to learn more about it, here is an article about The Elements and Principles of Design that will help you when compositing in Photoshop.