The easiest way is with a photo storage site that automatically generates an "embed" code for sharing on other sites. I use Flickr which is free (in the US, anyway); some people who are more organized like SmugMug which is a pay service. Once I upload the photo to Flickr and make it public, I choose the share button (curved arrow) and can select code to insert the image into an AP post.
Technically it's possible to use image tags if you have a photo posted on, say, your own website ...
https://www.w3schools.com/tags/tag_img.asp explains. The URL after src=" is the URL of the image, but that hasn't consistently worked for me.