Note of the name of the artist or photographer who created the work, the title of the work, the date it was created, the name of the repository, museum, picture agency or owner of the work, the city or country of origin, the dimensions of the work, the material or medium such as oil on canvas and the website and date of retrieval if acquired electronically.
Contact the rights-holder of the picture to confirm these details and seek permission to include the image in your work. If your work is academic or being published on a nonprofit basis, many museums, repositories, artists and photographers will negotiate nonprofit terms. If your work is going to be published, ask the rights-holder how they would like the work to be credited.
Talk to your tutor or editor about the house rules on style. A common format for image citation would take the form of the artist's name, followed by the the title of the work, possibly underlined or italicized, the institution or individual who owns the work, and the work's date.
Add footnotes relating to pictures in the format recommended on the same page they appear if possible.