By default, custom link images can only be used with manually shared links on FB fan pages. In this tutorial we will explain you how to assign a custom Facebook share image on per post basis in your WordPress site. Generally what happens is whenever any post link is shared, Facebook tries to grab images from the linked webpage. Many a times it allows you select a thumbnail, sometimes it fails to grab images and fetches only link title and description. In-case of auto posting; FB randomly grabs an image. All these things happens only on websites not using proper open graph meta tags.
Adding proper Facebook Open Graph Meta tags and values to your WordPres site gives awesome looks to the links of your website shared on Facebook. WP Facebook Open Graph protocol, a free WordPress plugin adds well executed and accurate Facebook Open Graph Meta tags details to WordPress.
The plugin makes things much easily by keeping minimal configuration and options but still it is a powerful Open Graph plugin and it not only works on Facebook but other networks like Google Plus and Linkedin.
Install and activate WP Facebook Open Graph protocol. After activation visit your admin area Dashboard -> Settings -> Facebook OGP page and enter your Facebook User ID or App ID for the plugin to work. Then you may add Default Image URL to use and that’s all.