Don't forget to accept your browser request to store data on the local computer!
If seen in Chrome run chrome with the following flags: --allow-file-access-from-files --allow-file-access in order to avoid a security error.
1. Open page locally (file:// in Chrome) or in Phonegap/Cordova
2. Work offline
3. Reload the page (or re-start the web app)
4. You should see the images reloaded from the cache
See console to check for any error.