Problem: Briefly: You have written a custom control which uses an embedded resource image, which does not show up on the ASP page.
Indepth: You have created a custom ASP.Net control which uses images. You have included images in your project and you have set them to be embedded resources.
And you load the images using "GetWebResourceURL". Like so - "Page.ClientScript.GetWebResourceUrl(this.GetType(), "ProjectName.FileName.ext");
You also verified that the method returns what looks like a valid url. (WebResource.axd? followed by a long string of characters). But you end up with the invalid image icon.
You check the dll in ILDASM and the resource is there.
And yet - it does not show up on your web page.
You look through the project properties and you scratch your head and you scratch your head some more - and you still can't make it work.
Solution: Here is what you need to do to make it work: It is called the "WebResourceAttribute" and the documentation says that it "Defines the metadata attribute that enables an embedded resource in an assembly."
So add following line in the AssemblyInfo.cs file. (One for each image that should be served from your dll).
[assembly: WebResource("ProjectName.ImageName.gif", "image/gif")]
The second attribute is the "content-type". (Valid values for this can be found at - http://www.iangraham.org/books/html4ed/appb/mimetype.html)