Downloading a macOS El Capitan ISO or DMG is primarily done for reviving older Mac hardware or setting up virtual machines. While Apple does not officially distribute an image directly, you can download a
: For users already running an older version of OS X (like Snow Leopard), El Capitan can sometimes still be found in the App Store under the "Purchased" tab or via direct links provided by Apple. Unofficial Community Repositories Mac Os El Capitan Download Iso Image