Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f6b19f2ced41d81826b26e5f5aa2dfca.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563