Best way to overlap portlets in Liferay?

I have an image that needs to appear behind my other portl开发者_高级运维ets, and ideally this image needs to be content manageable. I'm I right in assuming the only way to tackle this is to embed a Web Content portlet for the image and give it a lower z-index than other portlets(?)

<div id="column-1" style="position:relative;z-index:999">$processor.processColumn("column-1")</div>
<div style="position:absolute;z-index:1;top:0;left:0">$processor.processPortlet("56_INSTANCE_10000")</div>

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If it's really just an image it might be easier to define a dedicated folder in the Image Gallery and use Liferay services to retrieve the image inside your Liferay theme, using $serviceLocator.