Prevent users from using full size images on WordPress

h1-remove-full-image-size.php

/*
How to prevent users from using full size images by removing
the full image size option from WordPress image dialog.
*/
function h1_remove_full_image_size( $sizes ) {
	unset( $sizes['full'] );
	return $sizes;
}

add_filter( 'image_size_names_choose',
            'h1_remove_full_image_size' );