Use image as panel background

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http://askubuntu.com – I installed Ubuntu 12.04. In the good old days where customizing your Ubuntu had no limits it was no big deal to change the background of the panel to an image of your choice. How can i change the panel of my Adwaita Cupertino Unity L theme? Can anyone help me out here? I've tried to make the panel transparent. That really did not look very well. Its like the autohide of the application menu is just going black when not hovering the menu. So its under the White Title of the window (HowTos)