How can I get a BitmapImage from a Resource?
This MSDN page has all the information you might want to know about resource URIs in WPF (often called pack URIs). You're going to want to use relative URIs more often probably, so see Table 4, which should be of particular use.
If you want a briefer overview of resource (pack) URIs, see this blog post. It shows that syntax is indeed relatively simple:
pack://application:,,,/ResourceFile.xamlpack://application:,,,/ReferencedAssembly;component/ResourceFile.xamlHowever, there are a few quirks to work out (in my experience), so often finding the correct resource URI requires a bit of experimentation.