Every picture tells a story, according to the saying (and a song
by Rod Stewart). Does it, really? True, pictures typically convey
a richness unmatched by words alone, which triggers all sorts
of intuitive and rather immediate reactions in viewers' minds.
At the same time, they lack the declarative capacity of words:
they can illustrate but cannot—on their own—assert anything.
The stories they tell, if any, are in fact created by the viewers.
Powerful as they are, pictures are therefore always ambiguous:
one picture may suggest different stories to different viewers.
Few people realize how ambiguous their pictures are, however.
Because they know what story they are looking for, they readily
recognize it in any illustration they create and cannot imagine
that others might see another story in it. At best, they clarify
what the picture is in the titles of their slides or the captions
of their figures, but seldom what the picture means, that is,
what the viewers are supposed to notice about it (the so what).
Last summer, I came across a lovely example of how the story
can be made explicit with just a few words in the right place,
in the form of an ultrasound image sent to me by my friends
Goéric and Marie-Catherine from California. As you may have
experienced, ultrasound images can be so hard to decipher
when you do not know what you are looking at or looking for,
and so informative when you do. A short declarative sentence
suffices in this case to clarify both the what and the so what.