URI to local file relative to assembly

For example I have the following project structure:

Root\Core\Application.exe
Root\Modules\Assembly.dll
Root\Modules\Icons\Icon.png

My Application.exe loads the Assembly.dll. The Assembly.dll includes a WPF UserControl with an Image control. The Icon.png is not an embedded resource, it is a local file (Build: Content).

I tried every possible URI in the Source-Property of the Image Control, but it never shows the image :-(

<Image Source="Icons\Icon.png" />
<Image Source="pack://application:,,,/Icons\Icon.png" />
<Image Source="pack://application:,,,/Assembly;component/Icons/Icon.png" />

etc.

How does the URI have to look like?