Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/912a9abe8ba7d3e7b86bd6d334c9e91a.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563