Add custom image sizes to WordPress and make them available within the Media Library Attachment Display Settings options.

functions.php

<?php
//* Add custom image sizes to WordPress
add_image_size( 'featured', 690, 180, TRUE );
add_image_size( 'full_width', 960);
add_image_size( 'grid', 300, 150, TRUE );
add_image_size( 'small_thumbnail', 100, 100, TRUE );
add_image_size( 'micro_thumbnail', 75, 75, TRUE );

//* Make custom sizes available within the WordPress Media Library Attachment Display Settings
add_filter( 'image_size_names_choose', 'amn_image_sizes_choose' );
function amn_image_sizes_choose( $sizes ) {
	$custom_sizes = array(
		'featured'		=> 'Featured',
		'full_width'		=> 'Full Width',
		'grid'			=> 'Grid',
		'small_thumbnail'	=> 'Small Thumbnail',
		'micro_thumbnail'	=> 'Micro Thumbnail'
	);
	return array_merge( $sizes, $custom_sizes );
}