Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a4f23da5b0a7d94073c4f0b098955fe2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563