Add Alt to image where it's empty in WordPress through functions.php

Adding following code to functions.php will add page title as a image alt to img tag:

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function callback($buffer) {

preg_match_all('/<img (.*?)\/>/', $buffer, $images);
	if(!is_null($images)) {
		foreach($images[1] as $index => $value) {
			preg_match('/alt="(.*?)"/', $value, $img);
			preg_match('/alt=\"(.*?)\"/', $value, $img2);
			
			preg_match('/data-src="(.*?)"/', $value, $imgurl);
			$title = "";
			$image_url = $imgurl[1];
          
          	//get alt from url in WordPress
    		global $wpdb;   		
    		$query_arr  = $wpdb->get_col( $wpdb->prepare( "SELECT ID FROM {$wpdb->posts} WHERE guid='%s';", strtolower( $image_url ) ) );
    		$image_id   = ( ! empty( $query_arr ) ) ? $query_arr[0] : 0;

$title =  get_post_meta( $image_id, '_wp_attachment_image_alt', true );
			
            // if there is no alt then get page title as alt
            if( empty( $title ) ) {
        		$title = get_the_title();
    		}
			
			if(!is_null($images)) {
				if((!isset($img[1]) || $img[1] == '') || (!isset($img2[1]) || $img2[1] == '')) {
					
					$new_img = str_replace('<img', '<img alt="'.$title.'"', $images[0][$index]);
					$buffer = str_replace($images[0][$index], $new_img, $buffer);
				}
			}
		}
	}

return $buffer;
}

function buffer_start() { ob_start(); }

function buffer_end() { echo callback(ob_get_clean()); }

add_action('wp', 'buffer_start', 0);
add_action('wp_footer', 'buffer_end');