Add the following to the plugin’s Custom JavaScript section (Customize > Misc > Custom JavaScript):
$('#cff .cff-author-img img').attr('src', 'http://path-to-your-image.jpg');
Add the following to the plugin’s Custom JavaScript section (Customize > Misc > Custom JavaScript):
$('#cff .cff-author-img img').attr('src', 'http://path-to-your-image.jpg');