If you use an image for an assignment, or for 'educational use', you do not need to get permission from the copyright owner, but you still need to provide a citation.
However, if you use an image for advertising, a blog, card or similar, you must obtain permission from the copyright holder of the image, as well as providing a citation.
Give the name of the artist, the title of the artwork (in italics), the year it was made, and where it lives (museum, gallery, etc.). Add other information if you know it, such as the medium and the size.
If you found the image online, give the date you found it, as well as the date it was published/updated, and the URL.
If you found the image in a book, cite the book and page number.
Image citations are not included in your bibliography, just used for captions or notes.
Example 1 of caption for a photograph, sculpture, painting etc
Figure 1. Sally Gardiner, Solitude No. 4, 2014, inkjet print on canvas, 60 x 150 cm.
Example 2 of citing within the text of a paper
If illustration is included:
There are many paintings of the American West. Georgia O’Keeffe’s The Cliff Chimneys 1938 (Figure 1) is a famous one.
If illustration is not included
There are many paintings of the American West. Georgia O’Keeffe’s The Cliff Chimneys 7 is a famous one.
Example 3 of a note for an image found on the Internet
Example 4 of a note for an image found in a book
Examples 2-4 above from:
"How do I cite an image", CMDS Shop Talk (website), March 15, 2016, accessed Aug 16, 2018, http://cmosshoptalk.com/2016/03/15/how-do-i-cite-an-image/.