I want to display a background image
To display a background image you will need to setup your image on the background of the page and then make the gallery transparent. To set a background image on the page just use the page properties. To make the gallery transparent, set the wmode parameter in the property inspector to transparent and choose nothing as background color.
This is extra complimentary content which purpose is to show additional usage that is not part of the product, i.e. it suggests tips for extending the functionality of the product by the users themselves. It is provided "as is", without warranty of any kind, express or implied , including but not limited to the warranties of merchantability, fitness for a particular purpose and nonfringement of third party rights.
DMXzone does not take responsibility to support the suggested content to be fully compatible and working as intended and does not provide support for extended functionality which is not included in the current release of the extension.
It is highly recommended that only more advanced developers use it.