When links to your site are shared on Facebook, by default it uses an image from your site to preview your site. To setup a custom Facebook image in Showit 5, click on a page and then in the right panel click on “Advanced Settings”. Copy the following code and paste it into there.
<meta property="og:image" content="http://URL-TO-IMAGE" />
Next, upload the preview image to Showit. Export the image in JPG format with a size of 1200 x 630. Click on the link icon in the top corner to copy that link.
Then go back to your page advanced settings and paste that link over the “URL-TO-IMAGE”.
Publish your site and then go to the Facebook Debugger to get your image refreshed. Enter your website URL and click “Fetch new scrape information”. You should now see the image listed and links will use this new preview image.