Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/726b5357d59e341b38e4c3e112b1a592.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563