If this is your package structure
/res/Background/bg_menu.gif
and /res
is a source folder, then
/Background/bg_menu.gif
should be at the root of your classpath. As such, you can access it with
image = ImageIO.read(getClass().getResourceAsStream("/Background/bg_menu.gif"));
Note the leading /
. The rules for the path are explained in the javadoc.
If this doesn't work, then your application is not being built correctly with Netbeans. check the deployment.