Every Vidcast recording you create will default to display the first recorded frame as it's thumbnail within your library. The "Select Thumbnail" tab allows you to change that to any other frame from within the video. Simply move the purple window cursor located below the playback window to whatever frame you'd like and click save.
Note that after saving, you can always choose to revert back to the original via the option in the lower left corner.
Questions? Feel free to begin a chat with our support team or reach us at help@vidcast.io