Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/585a2b2cf12fec4f7484a8707f0e0f3a.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563