Appian Component Plugin document datatype parameter?

Hi. I want to build a component plugin that can display an image with som additional display parameters, i.e. the a!imageField() does not provide the settings/parameter that I want. 

I have made a simple component that uses the HTML tag <img> and can set the image source in Javascript like "img.src = 'pic' ". But how do I get an Appian document (image) sent to my component through the parameters? 

The list of valid parameters does not allow for type document to be sent. However it does include the types variant and dictionary that might seem generic enough to pass along an image with? See Component Plugin Configration File Parameter. 

Thanks,
Jesper.