Add custom image sizes to "Insert Media" in the content editor and add custom class to the tag.
<?php
function ccd_insert_custom_image_sizes( $sizes ) {
global $_wp_additional_image_sizes;
if ( empty($_wp_additional_image_sizes) )
return $sizes;
foreach ( $_wp_additional_image_sizes as $id => $data ) {
if ( !isset($sizes[$id]) )
$sizes[$id] = ucfirst( str_replace( '-', ' ', $id ) );
}
return $sizes;
}
add_filter( 'image_size_names_choose', 'ccd_insert_custom_image_sizes' );
?>
WordPress Snippet