Hi,
Yes, that’s possible. Please, follow the steps below:
1. Open the “/wp-content/plugins/cp-related-posts/cp-related-posts.php” file, with the text editor your choice.
2. Go to the snippet of code:
$image = wp_get_attachment_image_src( get_post_thumbnail_id( $related_posts[ $i ]->ID ), ‘single-post-thumbnail’ );
and replaces the ‘single-post-thumbnail’ text, by any of following strings:
‘thumbnail’
‘medium’
‘large’
or if you want an specific size used in your website, replace the previous string with an array with the width and height of the image. For example if you are cropping your images to 150×150 px, the code to use would be:
$image = wp_get_attachment_image_src( get_post_thumbnail_id( $related_posts[ $i ]->ID ), array(150,150) );
That’s all.
Best regards.