The logo and wideLogo options for
secondary tiles accept ms-appx:/// and ms-appdata:/// URIs for in-package images and those in your appdata local folder, respectively. Sounds like you’ll want to use the latter, which means downloading the image to local appdata, building the URI string
for the secondary tile, and creating the Windows.Foundation.Uri object for the options.
Scenario 1 of the
Secondary tiles sample shows how to use the ms-appx:/// URIs which you can easily modify to use ms-appdata:///.
Kraig
Author,
Programming Windows 8 Apps with HTML, CSS, and JavaScript,
a free ebook from Microsoft Press