thumbnail wordpress

add_image_size( 'thumbnail', 155, 78, true );
add_image_size( 'random-thumbnail', 133, 133, true );
add_image_size( 'gallery-thumbnail', 250, 200, false );
add_image_size( 'gallery-large', 660, 500, false );
add_image_size( 'gallery-pagethumb', 70, 70, true );