A link preview will generally be handled differently based on the social site you're posting to. Please see the list below for the relevant link preview information for different social sites and RSS Auto Posters:
Facebook has removed the ability to customize link previews. Please see the Why are changes to link previews not displaying when posted to Facebook? for more information.
How and when a link preview is displayed on Facebook is largely dependant on the settings you've selected when setting up or editing a Facebook posting service.
If you set the “Post as full-sized image” option to “No”, it will post the link preview as normal.
If you set the“Post as full-sized image” option to “Yes” and the link preview was automatically generated, then it will treat the link preview as an image. Also, links will no longer be stripped from the message as this would remove information from the message which would have been in the link preview.
Please note: If the“Post as full-sized image” option is set to “Yes” but the image displays as a normal link preview and not a full-size image, this means that the image was square or portrait in its dimensions and currently Facebook only supports full-sized landscape images.
If “Automatically generate link previews” option is set to “Yes” but a message has no photos or videos attached, the program will search for links in the body (text) of the post. It will then pull meta data (e.g. title, description and image) for the first link it comes across.
For more information on Facebook Page posting service settings, please see this page.
Twitter doesn't currently support link previews in the same way that Facebook and Google+ do for example.
Twitter's version of a link preview is called a 'Twitter Card'. Currently, Twitter Cards will only be displayed in a post if the site you're linking to has Twitter Card information available on the site itself which tells Twitter to display a Twitter Card.
The following page provides more information about Twitter Cards:
This means that we currently have no control over Twitter Cards and when they are or are not displayed however, we are hoping that Twitter will give third parties like Sendible access to Twitter Cards in future.
The only option we can currently provide which is similar is for images to automatically be pulled from links and for this to be included in your Twitter post.
If the “How link previews should be posted” option on the Twitter posting service your posting to is set to “Ignore images”, then Twitter will just ignore the link preview.
If the “How link previews should be posted” option is set to “Post with images”, then Twitter will post the image as long as this will not truncate (replace part of the text with '...' so it is not more than 140 characters) the message text.
For more information on setting up Twitter posting services, please see this page.
The most important thing to note with Google+ is that, if you choose for link previews to be included in posts you're sending to a Google+ page or profile (you'll need to set this in the service options), Google+ ignores all information we send through with regards to what image should be used in the link preview. This means that if you've selected another image than the first one brought up by default in the link preview or if you create a link preview from a custom image, this will not be reflected once the post is posted on Google+.
In terms of the available settings, if the “Use Google's link preview” is set to “No”, then Google will create a message where the image is a normal image and the title and description will be included in the body (text) of the post.
If the “Use Google's link preview” option is set to “Yes”, then Google will create a message with a Link Preview, however, as advised above, due to the limitations of Google’s link preview API (how we integrate with Google+) it will automatically select an image and ignore the image in the link preview.
For more information on setting up Google+ posting services, please see this page.
As with Google+, the image should be available on the page you're linking to as LinkedIn ignores link preview information sent by third parties like Sendible. Therefore, creating a link preview from an image or similar will not work in this case.
RSS Auto Poster
Link previews can be included on messages being automatically pulled from RSS Feeds and posted out via an RSS Auto Poster when the option “Post the following content” is set to “Title, Link and Image”, "Title, Description, Link and Image', or 'Description, Link and Image' on the RSS Auto Poster service settings.
In this case, our system will try to locate the image by initially searching for the OpenGraph image based on this protocol: http://ogp.me and then defaulting to the first image it finds in the web page the link goes to.
Image information can still be pulled if OpenGraph information is not set on the page you're linking to but, if you are the owner of the site, we would recommend adding OpenGraph information if you haven't already as this not only helps in this case but OpenGraph information is accepted by the majority of social sites such as Facebook and Google+ meaning you can control what information is being displayed in a link preview, even if the person posting is not doing this via Sendible or another third party social site.
For more information on RSS Feeds and RSS Auto Poster settings, please see this page.