My motivation for this question is really just to specify an image to be used in a user control via a dependency property for ImageSource. I'm hitting some pain points involving the management, access, and unit testing for this.
No, the resource editor is not a good tool for this.
In a WPF application the best way is to put all of your images in an "Images" directory and mark each one as a "Resource". Then you can reference them directly in Image controls and elsewhere.
Here are the precise steps:
Now you can reference your images easily in XAML:
<Image Source="Images/MyImage.png" />
Or in code:
var source = (BitmapSource)Application.LoadComponent(
new Uri("Images/MyImage.png", UriKind.Relative));
You can also reference images in external assemblies:
<Image Source="ReferencedAssembly;v1.0.0.1;component/Images/MyImage.png" />
Which in code would be:
var source = (BitmapSource)Application.LoadComponent(
new Uri("ReferencedAssembly;v1.0.0.1;component/Images/MyImage.png",
UriKind.Relative));