Changing product images and design options

Is there a way to change the default image on the design canvas? For example, if I wanted that shirt to be a red one that I have as a blank, how do I use that?

Also, can I configure this to allow me different options other than the ones you have listed? For example, I would like my customers to be able to design a framed poster, and would like to be able to use the image I have of a poster as their backdrop.