A simple solution that doesn't require a "Hack" or some complex linking system, to easily attach an image to a feature, have it show up in the pop up, and when I share the layer as a web-layer on AGOL, have the image upload as well and show up natively in the pop-up. There should also be an "Add Media" button somewhere either in the popup or in the attribute table to quickly do so. If you add multiple images, it should just automatically turn into a slideshow style.
Simply put, make it so I can add an image to a feature quickly, view it, and share it.