Well,
one picture is worth a thousand words.
P=1000W
You can derive that
.001 P = W
So in that sense, a word is worth .001 pictures.
However, it doesn't really work that way. A picture can be described extensively, with 1000+ words, as much as one word can bring to mind 1000+ pictures. Think "blue". You might see the sky, you might see the water, you might see jeans, you might see blueberries... There are thousands of images that come to our mind when we think blue, and that's why I think that it's arbitrary to say that a picture is worth a thousand words or a word is worth a thousand pictures. Words can be interpreted as differently as pictures can be, and therefore I have come to this conclusion.
P=W
Which, makes sense, since after all, a written word is no different than a picture.