While there are plenty of good quality images available on the web, don't forget that the Library's strong print collections offer an additional tens-of-millions of good quality visual materials, ranging from art reproductions to maps, drawings and photography.
To find books with illustrative content, simply do a search in BobCat and note the presence (or absence) term "ill." or "illus." in the NOTES field(s) of the record(s) retrieved.
This guide is intended for the researcher who needs to locate visual materials-- from reproductions of artworks to photographic images of just about anything imaginable. Bobst does not maintain a vertical file of art reproductions or other images, nor does it own slides. The Library does, however, have tens of millions of images of artwork, people, non-human beings and life-forms (microbes, plants, animals, extraterrestrials, etc.) events and phenomena spanning all periods, styles and cultures, in books, exhibition catalogs, periodicals and other print materials. Add to that the tens of millions of images freely available on the internet, and you might say that there is quite a picture collection here!
Before you begin your search, make sure you have a good idea of exactly what you're looking for. For example, must the picture be in color? If so, newer is better! All color reproductions change rather rapidly with age. It is uncommon to find an image in a book published as recently as the 1970s that has not undergone some fading or mutation.