Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/de0f67e4094bd2c983e62f79d75646d6.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563