Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a0f7a0e77e200e5437e173f2178e7576.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563