You don't need permission.
The original drawing is owned by the Galleria dellAccademia in
Venezia (Venice), Italy.
The drawing has been in Venice since 1815. Before that, it was owned
by Giuseppe Bossi, who published it in a volume of Leonardo's drawings
source: Ursus Rare Books, cached by Google:
Since drawing has been widely published over the last two centuries,
it is "public domain," which means that it isn't copyrighted, and you
don't need anyone's permission to copy it or use it.
"What is Art in the Public Domain?"
"The art is in the public domain if it was published in the United
States before 1923. Art is published for copyright purposes whenever
copies are made available to the general public -- for example,
photographs, postcards, prints, lithographs, castings from a statue
and other reproductions."
The only real issue here is whether you can copy someone else's
particular photograph or reproduction of Vitruvian Man. You might need
permission if you were talking about copying someone else's unusual,
altered, or creatively presented version of Vitruvian Man, but if
you're talking about a basic photographic reproduction, it's public
In the recent case of Bridgeman Art Library, Ltd. v. Corel Corp., 36
F. Supp. 2d 191 (S.D.N.Y. 1999), "the court ruled that direct accurate
photographic reproductions of two-dimensional artwork lacked enough
creativity to be original and thus protected under copyright law. The
original work may still be protected, but not the photograph. If the
art is in the public domain, no one may have legal rights to the
image. If the photograph did exhibit some originality such as in angle
or lighting, then it could qualify for copyright protection. A
photograph of a three-dimensional artwork might more easily qualify
due to choices of angle or other creative choices."
source: Copyright Law - Resources
BRIDGEMAN ART LIBRARY, LTD. v. COREL CORP., 36 F. Supp. 2d 191
As the court's opinion indicates, "substantially exact reproductions"
of public domain works of art are also public domain. Since Vitruvian
Man is a two-dimensional, public domain work of art, a basic
photographic reproduction would also be public domain. You are free to
use it on your web site or in your book without permission.
leonardo, "public domain"
"public domain", art reproductions
"public domain", "BRIDGEMAN ART LIBRARY", corel
As always, note that Google Answers provides general information.
This answer is not intended as, and should in no way be considered,
professional legal advice. No warranties are expressed or implied.
I hope this helps.