Many designers use Photoshop as a graphics editing tool or as a tool for creating website mockups. However Photoshop is primarily meant for digital photo editing. One such area of work is compositing which takes two(or more) photos and combines them together into one photo.
Compositing is a difficult skill to pickup but very powerful across many careers. It can be used to create banners, logos, book covers, or even print advertisements. The best way to learn compositing is through repetition and consistent practice. If you don’t know where to get started dig through some of these tutorials which cover very thorough methods of compositing.
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