It means the image is mounted flat to its decorative backing board or substrate.
Though generally dry mounted with a permanent adhesive, images may be wet glued, spray mounted or p-s mounted as long as the adhesive distribution may be controlled during application.
An image is a visual representation of something. It is a representation of something or someone or a photograph or an idea you're picturing in your head or the way you or others think of you. An example of an image is a painting of your father.
In science, An image may be defined as that point, where the light rays coming from an object meet or appears to meet after reflection or refraction.
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