Upload your own custom defaults to the below folders.
Canvas
/components/com_comprofiler/plugin/templates/default/images/canvas
Avatar
/components/com_comprofiler/plugin/templates/default/images/avatar
Next edit your canvas and avatar fields then change their defaults under Parameters > Image Display. Be sure to supply a thumbnail version of your images as well by having a smaller image with the same filename as the original image except prefixed with "tn".