When posting a Shared Link in Facebook, you may include thumbnail images in the items you share. These images will display on your Facebook page, right next to your content. This Facebook feature contrasts with Twitter, which only allows up to 140 characters of text (any images are hosted on other services and available via a link in the tweet). The addition of an image can enhance your content and engage users with a visual connection to your headlines and text.
How do I control which thumbnail is posted?
Auto-Detected by Facebook
When posting a Shared Link, Facebook will automatically detect an image from the page you are sharing and include the thumbnail in your post. Facebook retrieves the webpage that the posted URL links to and performs its own internal selection of which thumbnail to display. dlvr.it has no control over which images Facebook chooses for display, and they may come from any portion of the linked page.
If you have control over the content of the destination pages, you can also assist Facebook in its thumbnail detection by following the information located in the OpenGraph documentation.
Auto-Detected from Item Content
Many publishers embed images in their item content using <img> tags and prefer to use these instead of the images Facebook auto-detects. Using “Auto-Detect from Item Content” instructs dlvr.it will scan for <img> tags embedded in the item content and include the first valid image we find as the thumbnail. dlvr.it will automatically skip any images which are not at least 250x250 pixels to prevent the selection of social media chicklets and other structural icons.
If dlvr.it is unable to validate the images, no thumbnail will be used.
Some publishers and bloggers prefer to include the same image – say a logo or photo – with each Facebook post. Select “Manual” and enter the URL of your image. We’ll include this image with all items posted to Facebook. Facebook recommends thumbnail dimensions of at least 200x200, and dlvr.it will not allow images less than 50x50 to be used.
1.) Click the Social icon on the dashboard
2.) Scroll to Thumbnail Style and select Manual
Don’t want to include an image with your shared links? Select “No thumbnails” and we’ll post your content as shared links without thumbnail images.
The most reliable way to control the images included with Facebook posts is to include OpenGraph tags on your pages.
Here's more on OpenGraph:
If you have OpenGraph tags on your pages, you can select the 'auto-detected by Facebook' option above. Facebook will scan the page looking for images -- and include the 'best' image. Typically, Facebook will include the OpenGraph image (og:image).
Facebook Sharing Best Practices