I have a fk displaying it's data with RADIO as control.
Boostrap takes it and transforms it in a button group : nice, it works. But what if the field pointed by the fk is an image ? Could i display the image instead of the name of the image in thebutton ?
Thanks for any help.

I never tried that.
You can try to create a new JDom class for that, using the bootstrap buttons.
Of course, you will need to call html.fly.image inside in order to get the right image url.
It should not be difficult.