Add Image Sizes to Media Insert Dialog / Thickbox

gistfile1.php

add_image_size( 'example', 500, 100, false );

// Add Logo Size to Media Upload Dialog
add_filter( 'image_size_names_choose', 'namespace_image_size_names_choose' );
function namespace_image_size_names_choose( $image_sizes ) {
	$image_sizes['example'] = __( 'What You Want The Image Size To Be Called In The Media Uploader', 'namespace' );
	return $image_sizes;
}