Push the Portable Network Graphics (PNG) images to the browser’s cache using cache pushes. Then do a Channel Push, which would reference the Universal Resource Locator (URL) of the cached images.
Complete the following steps:
Perform a cache push, to push the unread icon to the browser's local cache. Set the HTTP headers as follows, then write the contents of the PNG file. This is similar to writing the contents of a page for a channel push.
Do another cache push for the read icon.
Do a channel push, using the URLs for the unread and read icons, above: