add_image_size( 'slider', 105, 105, true ); // the_post_thumbnail( 'slider' );
add_filter( 'image_size_names_choose', 'image_sizes' );
function image_sizes( $sizes ) {
$addsizes = array(
'slider' => 'Слайдер'
);
$newsizes = array_merge( $sizes, $addsizes );
return $newsizes;
}