Add custom image sizes to media insert dialog

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<?php

if ( function_exists( 'add_image_size' ) ) {
    add_image_size( 'new-size', 300, 100, true ); //(cropped)
}
 
add_filter('image_size_names_choose', 'my_image_sizes');
function my_image_sizes($sizes) {
        $addsizes = array(
                "new-size" => __( "New Size")
                );
        $newsizes = array_merge($sizes, $addsizes);
        return $newsizes;
}

?>

Instructions:

Add to your functions.php file to add new image sizes to the Upload/Insert dialog in WordPress.

Related links:

http://www.wpmayor.com/wordpress-hacks/how-to-add-custom-image-sizes-to-wordpress-uploader/