How do I change the default image that is used for Facebook sharing?
By default, Facebook will pull the image from the page when your client shares a registration, etc to Facebook. You can change the url of the image that will be used on the Online Registration -> Configuration page in the Admin Module. Just put in the url of the image and click 'Save' for that section. The url has to be a fully qualified url including the "http(s)://".The minimum image size should be: 600 x 315 pixels.
The recommended image size is: 1200 x 630 pixels.