In common usage, an image (from Latinimago) or picture is an artefact that reproduces the likeness of some subject -- usually a physical object or a person.
Images may be two-dimensional (e.g. a photograph) or three dimensional (e.g. a statue). They are typically produced by optical devices -- such as a cameras, mirrors, lenses, telescopes, microscopes, etc. and natural objects and phenomena, such as the human eye or water surfaces.
A volatile image is one that exists only for a short period of time, e.g. the reflection of an object by a mirror, a projection of the sun on a wall by a pinhole camera, or a scene displayed on a cathode ray tube. A fixed image, also called hardcopy, is one that has been recorded on a material object, such as paper or textile.
A mental image exists in someone's mind: something one remembers or imagines. The subject of an image need not be real; it may be an abstract concept, such as a graph or function -- or an imaginary entity or being.
In many other scientific and technical contexts, image usually means a two-dimensional signal -- a physical phenomenon that can be modeled as a function from a two-dimensional domain (such as the plane or a rectangle) to some set of values, usually real numbers or vectors. This sense covers not only digital images but also analog ones, such as photographs. See image processing.
In computer science the word image can also mean an exact (bit-by-bit) copy of the contents of some device, such as a hard disk, floppy disk, CD-ROM, etc.. In particular,
An executable image is a structured file containing machine instructions and data, which can be loaded into a process's virtual memory and executed. See kernel (computers).
In mathematics, an image is a value or set of values of a function. Specifically, let f be a function from the setX to the set Y. If a is an element of X, then its image under f is the value f(a). If A is a subset of X, then its image under f is f(A) = {f(a) : a∈A}. Finally, the image of f itself is f(X), i.e. the same as the range of f.
