Send articles on the subject of your book of photographs to magazines, if you're preparing an edition of someone else's photographs. For example, if you have created an edition of Diane Arbus photographs, you can send in articles on Arbus to mainstream magazines, piquing interest in her work. Some of the magazines that take an interest in photography are "Artforum," "ArtNews," and "PHOTO." This will also boost your own credibility.
Submit your photographs to museums or galleries if they are original works. Introducing your work to a larger audience can boost your credibility when pitching your work to a publisher.
Submit your photographs to magazines that emphasize contemporary work, such as "ArtForum" or "Tin House." Also, consider submitting your work to contests.
Contact agents with experience in the photography publishing world by sending a query letter or email. Agents have varying specialties; some represent contemporary artists and others work with academics preparing older editions.
You can find an agent who has worked on similar projects, or you can find large agencies such as Curtis Brown, Ltd. Most agents make their emails available online, or have a mailing address listed on their webpage. Correspondence with an agent should convey your knowledge of his previous work and a synopsis of your project and any relevant training and experience you have.
Send query letters to publishers. Taschen, Harry and Abrams, and Phaidon are major publishers of high-quality books of photography. Make sure that the queried publisher has not published something similar recently by surveying its online catalog.
A query letter should contextualize the manuscript, give an engaging summary of its contents, and give contact information and qualifications of the photographer.
Prepare the manuscript once you've gotten interest from publishers. Your manuscript should be scrupulously edited and researched.