Frank P. Walentynowicz

Setting featured images for posts / pages could be very time 
consuming, especially when your media library holds hundreds of 
pictures. Very often we select the same thumbnail for posts in 
particular category. This plugin automates the process by inserting a 
thumbnail based on category / thumbnail mapping while post / page is 
being created or updated. Now bundled with FPW Post Thumbnails.

FPW Category Thumbnails

Assigns a thumbnail based on categoryid/thumbnail mapping to a post / page when the post is created or updated. Built-in FPW Post Thumbnails.

Ajit Kumar Satpathy

These must be in function.php in the theme for the plugin to work for thumbnail and excerpt:
add_theme_support( ‘post-thumbnails’ );
set_post_thumbnail_size( form_option(‘thumbnail_size_w&&echo=false’), form_option(‘thumbnail_size_h&&echo=false’), true );
function custom_excerpt_length( $length ) { 
 return 20; 
} 
add_filter( ‘excerpt_length’, ‘custom_excerpt_length’, 999 ); 
function custom_excerpt_more( $more ) { 
 return ”; 
} 
add_filter( ‘excerpt_more’, ‘custom_excerpt_more’ );
You’ll also need to add thumbnails to the posts you want visible in the list.
After that, all you need to do is to add the hook [getcatlist 1] (where 1 is a categoy id) to your post.

Category Thumbnail Excerpt

Lists a category with thumbnails,title,excerpt with a read more link

FPW Category Thumbnails vs Category Thumbnail Excerpt