Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/1d75bb3fb3c2af58b637a2aa3eb0b5b3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563