Wordpress - Image showing on the online page, but when going in admin, i cannot find where it is specified?

I just got to continue a wordpress website that a past employee started. I am totally new to wordpress.

The thing is, I am trying to understand how all elements are setup in the admin side so that it looks as is online. I am getting difficulties finding a particular image that is present in a post of my homepage right under the title, but when I am going in the admin mode to edit my post, there are no images at all.

Still didn't figured out how the media section alone could link images to a post, but sure thing, the image is not inserted directly in the post because there is nothing showing that the past employee used the 'add media' button to add it (no code related to images).

So, what could help me (since I can't post images) is telling me the ways the past employee could've add this image there, and how to manage it so I can change the image. Did he wrote some custom code somewhere? or am-I just missing something?