how do i get the image selected when using filebrowser : 'in

Hello,
I have a plugin that opens an Iframe dialog.
I would like to use the filebrowser for the use to select an image.
so, in my contents: i added

{
type : 'button',
id : 'browse',
hidden : 'true',
filebrowser : 'info:url',
label : 'Browser Server'
}

and when i click the browser server (which is ckfinder) , it opens OK

My questions i do not understand where the info goes when the user selects the image in the browser.

So i need to create some kind of listener?

Thanks for any help
Randy