Image don't display in Modern UI for WPF c#

I'm developing a Modern UI app for WPF c# , the problem is the Image displays only in mode design , when I execute the app ,  it doesn't show.
I added ""pack://siteoforigin:,,," but it doesn't work.
Anyone can  help me please!

Code:

<Image Source="pack://siteoforigin:,,,/Image/back1.png"/>

Thank you