What does Boxing Day have to do with boxing?
early 15c., "drawing, painting," 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 first recorded 1899. Phrase every picture tells a story first attested 1900, in advertisements for an illustrated life of Christ. To be in (or out of) the picture in the figurative sense dates to 1900.
Expression a picture is worth a thousand words, attested from 1918, probably was from the publication trade (the notion that a picture was worth 1,000 words is in printers' publications by 1911). The phrase also was in use in the form worth a million words, the form used 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." It 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.
late 15c. in the literal sense; 1738 in the mental sense, from picture (n.). Related: Pictured; picturing.