Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/436a7d0b8379a167cf20b6770367c2d4.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563