HTML
This is an <img> tag, and the src is in the master: 
This is an <img> tag, and the src is not in the master: 
This is an <iframe>, and the src is in the master:
This demo goes with the article "Optimising SVG load with Service Worker".
If it works, you should see green dots on all images but the heart one.
Supported browser: latest Chrome (Desktop and Android), Firefox (only got it to work on Developer Edition) and Opera.
The first time the site runs, it will install the Service Worker, so it won't be ready right away: none of the images will have a green dot.
The next reload, the SW should be installed and running, and the images should have the green dot.
This is an <img> tag, and the src is in the master:
This is an <img> tag, and the src is not in the master:
This is an <iframe>, and the src is in the master:
The SVG images processed by the Service Worker show a green dot on the top left corner.
Icons from small-n-flat set.