"Posters have been
a powerful force in shaping public opinion because propagandists have
long known that visual impressions are extremely strong. People may
forget a newspaper article but most remember a picture. A pamphlet or
a newspaper can be thrown away, unread; the radio or television turned
off; films or political meetings not attended. But everyone at some
time or other notices messages when walking or driving, or sees posters
on bulletin boards in offices, hospitals, clinics or pharmacies. The
main objective of posters, as with other communications media is to
influence attitudes, to sell a product or service or to change behavior
patterns. Public health posters are clearly in the third category, their
purpose being to alter the consciousness of the public to bring about
an improvement in health practices."
-- William H.
Helfand, To Your Health: An Exhibition of Posters for Contemporary Public
Health Issues, National Library of Medicine