Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2571a0a18d5f48754a00bb27941bef43.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563