Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6c52345090f5d3693dcb2e06e41c554a.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563