I'm wondering if its possible to add a button on top of an image?
Cheers

Yes, there are various ways of doing this. One way is to use a background image. Alternatively you can use position: absolute for the button and position it anywhere. Make sure that the parent (column or container) containing the picture and button is positioned relative. This gives the button the coordinate system for positioning it using the values below the position control in RSD. If the button is not visible (behind the image) just increase the z-index.