To provide an image to be used when a link to your site is posted on Twitter or Facebook you can to use special meta tags.
Example rom the fly.pieter.com website
<!-- Open Graph / Facebook -->
<meta property="og:type" content="website">
<meta property="og:url" content="https://fly.pieter.com/">
<meta property="og:title" content="fly.pieter.com">
<meta property="og:description" content="A fun free-to-play MMO flight sim, made with AI. Fly and dogfight with your friends online.">
<meta property="og:image" content="http://fly.pieter.com/assets/fly_social_image.png?1234">
<!-- Twitter -->
<meta property="twitter:card" content="summary_large_image">
<meta property="twitter:url" content="https://fly.pieter.com/">
<meta property="twitter:title" content="fly.pieter.com">
<meta property="twitter:description" content="A fun free-to-play MMO flight sim, made with AI. Fly and dogfight with your friends online.">
<meta property="twitter:image" content="http://fly.pieter.com/assets/fly_social_image.png?1234">
<link rel="icon" type="image/png" href="https://fly.pieter.com/assets/fly_emoji.png">
<!-- Hide iOS Share popup -->
<meta name="apple-mobile-web-app-capable" content="yes">
USEFUL?
We benefit hugely from resources on the web so we decided we should try and give back some of our knowledge and resources to the community by opening up many of our company’s internal notes and libraries through mini sites like this. We hope you find the site helpful.
Please feel free to comment if you can add help to this page or point out issues and solutions you have found, but please note that we do not provide support on this site. If you need help with a problem please use one of the many online forums.