Here are some examples/models for citation formats for images. In each case, you should put the citation in the “caption” window, which you can find when you upload or edit on “Media.” As you upload more images, make sure to put your citations in there.
You’ll also need to consider whether you need permission to use images you get online. If an image (or a text) was created before 1925, it is automatically in the public domain, which means you don’t need permission to use it. If it was created after that, your need to acquire permission (or to make a “good faith effort” to do so) will depend upon where you found it.
All images must have citations/captions, including those that you’ve taken yourself. (“Photo by [your name]”) You want to do this not only because scholars must cite their sources, but also for the sake of clarity: you want your reader to know what they’re looking at, and where the image came from. Presenting an image without explaining its meaning and purpose can be confusing and misleading.
Please let me know ASAP if there are any other types of image-based primary sources you’re confused about how to cite. I will add to this post as they come up.
Sanborn Maps:
Make sure you include the correct sheet #. No permission needed.

Corner of Edgewood and Bell, Atlanta 1911-1925, sheet 453, Sanborn Fire Insurance Maps.
Snapshots from Birdseye Maps:
You can find three different birds eye maps of the Atlanta if you go to the Library of Congress website (www.loc.gov) and search for birds eye map Atlanta. You do not need permission to use any of them — they’re all in the public domain. But make sure you cite them, using the correct date and contributor.

Flatiron Building, Foote and Davies Birdseye Map of Atlanta (1919)
Photographs from the GSU Library’s Digital Collections:
You can find the accession/catalog # if you scroll down the page on the Digital Collections website. You do not need permission to use them, but you must give a full citation.

“Wreckers expose the oldest building in downtown Atlanta, the Georgia Railroad Freight Depot, Atlanta, Georgia, October 30, 1979.” AJCP201-15b, Atlanta Journal Constitution Photographic Archives. Special Collections and Archives, Georgia State University Library.
Photographs from the Atlanta History Center:
Here, too, you can find the catalog # by scrolling down the page on the AHC Album website. You don’t need permission as long as you’re using the version of the image with the AHC watermark.

Kimball House (c. 1950), VIS 82.582.04, Kenneth Rogers Photographs, reproduced with permission from Atlanta History Photograph Collection, Kenan Research Center, Atlanta History Center, Atlanta GA.
Images from Wikipedia or Wikimedia Commons:
If an image appears on Wikipedia, it is possible that the owner of that image has released it to the public domain. If that’s the case, you can use it without permission … but you still need to cite it.

The Richards Mausoleum, Oakland Cemetery, Atlanta GA. Image from Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Oakland-Cemetery-Richards-tomb.jpg (accessed April 5, 2016)
Images from Archival Collections:
This image comes from the Breman Jewish Heritage Museum in Atlanta. It was sent to me by their archivist, and he gave me permission to use it.

Menu (c. 1960), Leb’s Restaurant Records, William Breman Jewish Heritage Museum, Atlanta GA.
Photographs that you took:
Of course, you don’t need permission to use a picture you took, since you took it. If there are people in the picture besides yourself, though, you should get permission from them. In the caption, state what it is a photograph of, if it’s not obvious to the reader. You can give it the caption “Photograph by author,” or you can attach your name to it. Either way, give the date that the photo was taken.

Mailbox in Rhodes-Haverty Building, Atlanta GA. Photograph taken by Marni Davis, January 7, 2016.