Layers and Masks

Many graphics applications are capable of merging one or more individual images into a single file. This is 'photo merging' or compositing; placing one or more items/images into another photo,
combining multiple images . Placing a person into your image;or even taking someone out,  is very useful for big events such as special gatherings. Family members may have been missing for example. Weddings are big occasions and good examples of where compositing/ photo merging is a great idea, and ,many customers approach a photo retouching company for this sort of work, and indeed we have carried out lots of work in this field.
A really powerful tool for collaging and compositing in Photoshop is using masks and layer masks. When we want to combine photos, we combine layer masks and gradients.
Layers are probably the single most important addition to Photoshop , but layer masks are a close second. I would say that until you thoroughly understand how and why to use masks, you simply don’t understand the power of Photoshop.
Layers are probably simply best described as individual sheets of transparrent paper. If you were to draw or place a seperate image on these sheets, you could quickly build up one image by placing these 'layers' on top of each other. Compositing.
There are two primary types of masks: clipping masks and layer masks.
The term “mask” isn’t immediately understandable to someone outside the realm of graphic design.Layer masks and clipping masks are closely related , but very different in application. Let’s start by discussing layers masks, which are generally what people are referring to when you hear them discuss Photoshop masking.
A layer mask is something that you apply to a given layer to control the transparency of that layer or a specific item on that layer. This is what you would use to remove an object from view.
You are just masking the object from view.
When you add a mask to a layer, On this invisible 'sheet', you can then  paint white, black or any level of gray in-between. The color that you paint tells Photoshop whether to make this visible or invisible from view. Painting black on a layer mask will remove the image. But unlike just simply deleting this destructively and permanently from your image, you can paint over the area again with white, and the area will be shown again. This is why you mask when editing images instead of removing or deleting.
At its simplest definition a mask is a way to apply something to a very specific portion of an image, 'masking' part of the image from view, like erasing; but importantly, unlike erasing, the edit is not permanent and can still be changed at any time.
Clipping masks are very similar to layer masks only they use one layer to determine the transparency of another. In this scenario, you stack two layers on top of each other with the bottom being the determining factor of the transparency of the top.
Its harder to explain without an example. See the below images:

Text is placed over background

A picture is placed under  the text

The layer is then 'clipped', and the final result is seen above

The orientation and placement of each image can be controlled for merging images together.
When selecting a raster image that is not rectangular, it requires separating the edges from the background, also known as silhouetting. This is the digital analog of cutting out the image from a physical picture. Clipping paths may be used to add silhouetted images to vector graphics or page layout files that retain vector data. Alpha compositing, allows for soft translucent edges when selecting images. There are a number of ways to silhouette an image with soft edges, including selecting the image or its background by sampling similar colors, selecting the edges by raster tracing, or converting a clipping path to a raster selection. These are all good ways for extraction or selection in the image editing process.
Much is down to the photo editor and their personal preferences.
Once the image is selected, it may be copied and pasted into another section of the same file, or into a separate file. The selection may also be saved in what is known as an alpha channel. If you are lost now, maybe you can see why it's best to rely on professional photo editing for this!
A popular way to create a composite image is to use transparent layers. The background image is used as the bottom layer, and the image with parts to be added are placed in a layer above that. Using an image layer mask, all but the parts to be merged are hidden from the layer, giving the impression that these parts have been added to the background layer. Performing a merge in this manner preserves all of the pixel data on both layers to more easily enable future changes in the new merged image. Think of it as sheets of tracing paper, placed on each other in layers to make up one image. Layers are a fundamental and important  part of photo editing, enabling non destructive editing of originals.
Another good use of photo merging- or compositing, is to create posters. Poster design is another service that we provide at Neilsonand son. We can provide a bespoke design for you at your request. Its just another example of the great photo editing services that we provide.