You need to serve your resource files (images, js, css, ...) in a static way.
To do this, put them in a subdirectory, then add this before server.listen
app.use(express.static(__dirname + '/public'));
(Assuming public is the name of the folder containing your static files)
Then, assuming your picture is called logo.png you can call it like this :
<img src="/logo.png" />