An inversion such as "a word is worth a thousand pictures" is described as an implied chiasmus by Wordsmith.org founder, Anu Garg, here, quoting these immortal words of Kermit the Frog:
Time's fun when you're having flies.
A chiasmus is "a rhetorical inversion of the second of two parallel structures." In the link, which is well worth reading, the examples of the inversion are of the sort: "Ask not what your country can do for you; ask what you can do for your country." So the implied chiasmus would be simply the second part, where the first (unspoken) one is the better known aphorism ("time flies when you're having fun" or "a picture is worth a thousand words").