Rename file on upload inside post

media-rename.php

function wpsx_5505_modify_uploaded_file_names($arr) {

		// Get the parent post ID, if there is one
		if( isset($_REQUEST['post_id']) ) {
			$post_id = $_REQUEST['post_id'];
		} else {
			$post_id = false;
		}

		// Only do this if we got the post ID--otherwise they're probably in
		//  the media section rather than uploading an image from a post.
		if($post_id && is_numeric($post_id)) {

			// Get the post slug
			$post_obj = get_post($post_id);
			$post_slug = $post_obj->post_name;

			// If we found a slug
			if($post_slug) {

				$random_number = rand(10000,99999);
				$arr['name'] = $post_slug . '-' . $random_number . '.jpg';

			}

		}

		return $arr;

	}
	add_filter('wp_handle_upload_prefilter', 'wpsx_5505_modify_uploaded_file_names', 1, 1);