By using Open Graph tags you can control how facebook shares your information. These are like
<meta> tags that you add to the
<head> of your website to describe your page.
If you use, Open Graph tags, the following six are required:
og:title– The title of the entity.
og:type– The type of entity. You must select a type from the list of Open Graph types.
og:image– The URL to an image that represents the entity. Images must be at least 50 pixels by 50 pixels. Square images work best, but you are allowed to use images up to three times as wide as they are tall.
og:url– The canonical, permanent URL of the page representing the entity. When you use Open Graph tags, the Like button posts a link to the og:url instead of the URL in the Like button code.
og:site_name– A human-readable name for your site, e.g., “IMDb”.
fb:app_id– A comma-separated list of either the Facebook IDs of page administrators or a Facebook Platform application ID. At a minimum, include only your own Facebook ID.
An Open Graph tag looks like this:
<meta property=”og:tag name” content=”tag value”/>
If you are just concerned about the image Facebook will grab and don’t want to deal with all involved in Open Graph tags, you can use the following meta key in your <head>
<link rel=”image_src” href=”path_to_your_thumbnail_image” / >