When reusing an image, you need to provide a caption under the image giving credit to the creator or provider. This is a bit different from referring to a visual work when you do not reuse the image.
“Whenever a public domain work is used, the author(s) (if known) should be cited. Citation may be made in accordance with any relevant scientific, scholarly, disciplinary, or community practice. Additionally, if a public domain work has been curated or made available by a person other than the author, that provider should also be appropriately credited.”
What do you need to cite? All attributions (even those for Public Domain or Creative Commons images) should have the same basic information:
* Title of image
* Creator name
* Source of the image (usually in the form of a URL to image source page)
* Any copyright information included with an image (such as a watermark)
* Creative Commons license information (including a link back to the Creative Commons documentation page if possible)
In the shortest caption allowed by the above, you would put:
caption: Title [hyperlinked to source] (c)Creator, License information [hyperlinked]