When preparing a new contest depending on what template is being used or if you have customized your template html your social share image may not display correctly or not display at all at the on the share window the users get after the login to Facebook, Twitter or any other social network that supports share images.
To customize what image you like to display as a "Share Image" for all social networks you need to have a div element with a class of "wcc-featured" and within that div element you can create an image tag that will display as the Share image, like so:
<div class="wcc-featured"> <img src="/path/to/my/share/image/here" /> </div>
You can enter this code on the contest template you are using by going to: Contests -> Templates then selecting the template your contest is currently using.
Make sure you know at least basic HTML and be careful while editing contest templates. Too many changes on it could break the functionality for the contest. We highly recommend testing the changes to templates in small increments (so if something breaks, you or your designer knows what was the change that broke the contest page).
Always save a backup copy of your templates in case you need to go back to your original.