The well-respected manual "Gray's Anatomy" is an excellent resource for medical pictures of the male anatomy. The textbook, first published in 1858, is considered to be the standard bearer on the subject of human anatomy and physiology.
Since it has been revised many times to the present day, "Gray's Anatomy" features illustrations and information on the human body that reflect the most modern medical knowledge. The newest versions are available for purchase both in print and electronically. The 1918 version is in the public domain, so it can be referenced without purchase. Many other pieces of medical literature -- both presented for the medical professional and the lay person -- available to the public contain photographs of male anatomy.
Organizations that target public education about sexual health, such as the Association of Reproductive Health Professionals, Planned Parenthood and the Family Planning National Training Centers, can be resources for visual aides to male anatomy.
Online sources for photographs and diagrams of human anatomy include websites such as WebMD, which has a slide show of common men's health concerns; The U.S. National Library of Medicine, which hosts a website featuring illustrations of male body parts; and the Centers for Disease Control and Prevention, which discusses many concerns related to male reproductive anatomy.