Photo masking is a technique used in graphic design and image editing to isolate a particular part of an image. It involves creating a mask or a layer that blocks out certain areas of an image, while allowing other areas to remain visible.

This technique is often used to remove the background of an image or to isolate a specific object within an image. For example, if you have a photo of a person standing in front of a busy background, you can use photo masking to remove the background and focus on the person. This technique can also be used to create a composite image, where different elements from multiple images are combined to create a new composition.

There are different types of photo masking techniques, including:

1.         Layer Masking: This involves creating a mask layer over the original image and then painting or erasing areas of the mask layer to reveal or hide parts of the underlying image.

2.         Alpha Channel Masking: This involves creating a selection based on the color or tone of an image, and then using that selection to create a mask.

3.         Clipping Masking: This involves using one layer to create a mask for another layer. The bottom layer is used as the base, and the top layer is used as the mask.

Photo masking can be a time-consuming process, and requires a certain level of expertise in graphic design and image editing software. It is often used in professional settings, such as in the creation of advertising materials or product photography.