Some Photobooks includes images, texts or documents from other authors or institutions, but they tend to acknowledge where this information comes from, as it happens in And you, why are you black? by Rubén H. Bermúdez. In this case, the visual artist lists all the images at the end of the book, indicating the page.
Therefore, if your Photobook includes images not created by you, you must reference the source, either on the page itself, at the end or both.
How to cite an image
Turquoise street, Matthieu Sévère, CC BY 2.0, https://flic.kr/p/dN3Eci
Title, Author, License, URL
How to cite other sources (articles, books, press…)
Consult the library’s Referencing guide.
Image Theory 