<Image Source="ms-appx:///Assets/Windows_10_Hero.png"/>
Your image is part of the application, in the Assets folder and marked as Content
<Image Source="ms-appdata:///local/Windows_10_Hero.png"/>
Your image was saved in your application's Local Folder
<Image Source="ms-appdata:///roaming/Windows_10_Hero.png"/>
Your image was saved in your application's Roaming Folder