Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a7d138833c4e7a1dff5d46edf2a696f9.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563