early 15c., pictur, pictoure, pittour, pectur, "the process or art of drawing or painting," a sense now obsolete; also "a visual or graphic representation of a person, scene, object, etc.," from Latin pictura "painting," from pictus, past participle of pingere "to make pictures, to paint, to embroider," (see paint (v.)).
Picture window is from 1938. Picture post-card is recorded from 1899. Picture-book, "book illustrated with pictures or consisting mostly of pictures," especially one for children, is by 1847. Picture-frame "more or less ornamental border put around a picture to protect it" is from 1660s.
The phrase every picture tells a story is attested from 1900, in advertisements for an illustrated life of Christ. To be in (or out of) the picture in the figurative sense dates to 1900.
The expression a picture is worth a thousand words, attested from 1918, probably originated in the publication trade (the notion that a picture was worth 1,000 words is in printers' publications by 1911). The phrase was used in the form worth a million words by American newspaper editor Arthur Brisbane (1864-1936) in an editorial much-read c. 1916 titled "What is a Good Newspaper" in the "New York Evening Journal." In part it read: "After news and humor come good pictures. In this day of hurry we learn through the eye, and one picture may be worth a million words."
The phrase seems to have emerged into general use via the medium of advertising (which scaled down the number and also gave the expression its spurious origin story as "a Japanese proverb" or some such thing, by 1919). Earlier various acts or deeds (and in one case "the arrow") were said to be worth a thousand words.
"[T]he only generally surviving senses on the Continent are 'to be worth; to be valid, to concern, apply to,' which are not represented at all in the English word" [OED]; sense development in English comes via use of this word to translate Latin reddere, French rendre. Sense of "give in return for labor or capital invested" is from early 14c. Intransitive sense of "give oneself up, submit, surrender (to a foe)" is from c. 1300. Related to Middle Low German and Middle Dutch gelt, Dutch geld, German Geld "money." Related: Yielded; yielding.
early 15c., "equal in value, power, or effect," from Late Latin aequivalentem (nominative aequivalens) "equivalent," present participle of aequivalere "be equivalent," from Latin aequus "equal" (see equal (adj.)) + valere "be well, be worth" (from PIE root *wal- "to be strong"). As a noun from c. 1500, "that which is equal or corresponds to." Related: Equivalently.