Image shows in Expression Blend but not during runtime

The image in question is located in a ControlTemplate inside of a ResourceDictionary similar to this (various details removed for clarity):

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006">
    <ControlTemplate x:Key="ImageTestTemplate" TargetType="ImageTest">
        <Grid>
            <Image Source="/MyAssembly;Component/Images/MyImage.png"/>
        </Grid>
    </ControlTemplate>
</ResourceDictionary>

When I view the control in Expression Blend the image shows up just fine, but when I run the app the image does not show up. If I drop the same ima开发者_JS百科ge into a UserControl it also shows up just fine, so the problem has something to do with using the template.

Is there some other way I should be loading the image resource inside the template?

---

I don't think you need the leading '/'. The base resource path I'm using for a project is "IMLPrototype2;component/Model/Sounds/" in SL 3 & 4.