You can't exactly USE their art page on here. You can't
right click on their art and save it, so it doesn't
matter.

But if you use it on a different site,
like dA, best idea would be no note them, and ask them if
you can. No one likes someone who just uses it without
permission.

^^
just what,i was
going to say draco,

If you mean on this site, PMs are the best way. Or if it's
another site, either email or if that site has private
messaging. But you're not supposed to use someone else's art,
even with their permission. If you are just going to
reference the images of that/those artists, you must give
the proper original copyrights.