Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/166b1d71b2624de97bdb04f0f1f32c7f.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563