While attribution and citation are often used interchangeably, they have subtle differences. Attribution is usually more focused on giving credit to the source of images, texts, ideas, etc., while citation is more focused on helping scholars trace back ideas through their development in various scholarly and primary resources. There is no single way to provide attribution, while citations are usually very regimented, with specific requirements and structure, depending on what citation style you are using. Both are acknowledging that someone else contributed content that you are using in your material.
There are best practices for giving attribution This is different than citing a source in a bibliography or works cited page. There is no correct way to attribute, but there are better ways than others. Ideally, in a digital project, if you are using images you found online, you link to the original image, the author's page, and the license, whenever possible. The idea is to give as much information as possible so someone else can find the image. At the very least, you need to have a link to the original image.
So what is going on in the above image and attribution? The first link is a link to the Flickr page where I found the image. The second link is a link to the author's Flickr page (you can find these by clicking on the author's name, then copying the link). The last link is a link to the CC license, which in Flickr you can find by clicking on the link that usually says Some rights reserved.
This is just an example from Flickr, other sites may be similar. As with many things on the Internet, not every author uses a proper name, so if they use a screenname or something that is obviously fake, still use that, since it is how they asked to be credited.
Wikimedia Commons makes attributing images easy.
Images that you have taken yourself and uploaded directly to a project can be handled as easily as:
Photo by Abraham Lincoln (Own work)
If you put the image on Flickr or another online repository, or added a Creative Commons license, you can treat it like any other image. Adding a title to the image may help identify it.