I did find this older thread Discussion: Content Organization Best Practice which weighs both options. It seemed like it was user preference with pro/cons on both sides, although in the very last post before the thread was closed, @alexandros, who seemed like he originally preferred having images in the static folder,
Page Bundles and image processing is the way forward to proper content management.
So it sounds like grouping images and content together in page bundles is now the preferred method, am I understanding that correctly?
It is the simplest way to manage images in a Hugo project.
If for some reason, you need to have them in a separate folder -like for example for Forestry or some other service- images will need to reside under the assetDir so that you can get them as resources on the fly with the method resources.Get