[Wordpress] Crop immagine in evidenza - Crop post-thumbnails

[Felino]

Risolto,
la dicitura corretta è:

if (function_exists( 'add_theme_support')) {
    add_theme_support( 'post-thumbnails');
}    




    if ( function_exists('add_image_size')) {
        add_image_size( 'full-size',  9999, 9999, false );
        add_image_size( 'slider',  980, 9999, false );
        add_image_size( 'portfolio-single',  550, 9999, false );
        add_image_size( 'small-thumb',  50, 50, true );
        add_image_size( 'grid-thumb',  230, 180, true );
    }

Successivamente, ho installato il plugin Regenerate Thumbnails (http://wordpress.org/plugins/regenerate-thumbnails/) e rigenerato le miniature.