CG Calendar - upload field

[spngg]

Hi, I've installed and started developing with the CG calendar module (great module btw).  I'd like to add a custom field which allows a user to select an image from library of already uploaded images.  I've seen there is an option called "file upload" but this allows a user to upload an image from their HDD and not select one from the existing library.  Anyone know a solution to this?

Thanks