Best way to implement a "Read Later" feature

Hello, I’m developing an app to read content from a news website.
Under every content I add a button “Read Later” and in my idea this button save the content for offline and add the content to an index.

When the application detect (using Cordova) the “offline” using the router I redirect to a “offline” view with the list of the saved content.

I can use LocalStorage for my index and for every json id, but I cannot find a way to manage the images.

I have a “main” image exposed as a url in my json and also a lot of images in an HTML fragment, the body of my content.

Is there an easy way to cache offline an HTML fragment saving also images in base64 format?