As Facebook only provides large image sizes in their API for timeline feeds then it often results in images being displayed in your feed which are much larger than needed. In the Custom Facebook Feed Pro plugin (v3.14 and above) the plugin will create resized versions of the larger images and store them locally on your server. It will then select the optimal sized ones to display in your feed.
As the Facebook API has images available which are 130px and 720px wide then the plugin will create images at sizes between these which are more optimal for your feed. The default sizes are 250px and 400px.
These image sizes can be changed by using the
cff_resized_image_sizes filter. An example is below:
$image_sizes = array( 400, 250 );
$this->image_sizes = apply_filters( 'cff_resized_image_sizes', $image_sizes );