The illustration in a book that faces the title page is called a “frontispiece.” Among book collectors and booksellers, this is often abbreviated to “frontis.”
Often this and other illustrations are printed using a halftone process on clay-coated glossy paper. They are inserted or “tipped in” at the time of signature gathering or binding.
Sometimes in higher quality/more expensive books the frontispiece (and perhaps other illustrations) will be protected by a page of thin tissue to keep the illustration from touching the facing page directly. Series books generally were not made with expensive additions like this.