From CS2800 wiki

Definition: Image
If [math]f : A \href{/cs2800/wiki/index.php/%E2%86%92}{→} B [/math], then the image of [math]f [/math] (written [math]\href{/cs2800/wiki/index.php?title=Im&action=edit&redlink=1}{im}(f) [/math]) is the set of values that are output by [math]f [/math]. Formally, [math]\href{/cs2800/wiki/index.php?title=Im&action=edit&redlink=1}{im}(f) \href{/cs2800/wiki/index.php/Definition}{:=} \href{/cs2800/wiki/index.php/Set_comprehension}{\{y ∈ B \mid} \href{/cs2800/wiki/index.php/%E2%88%83}{∃x} \href{/cs2800/wiki/index.php/%E2%88%88}{∈} A\text{ such that }y=f(x)\} [/math] or more succinctly, [math]\href{/cs2800/wiki/index.php?title=Im&action=edit&redlink=1}{im}(f) := \href{/cs2800/wiki/index.php/Set_comprehension}{\{f(x) \mid x ∈ A\}} [/math].

Some authors use the term range to refer to the image; I tend to avoid this term, because others use it to refer to the codomain.