Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/b4f89bf3c459bb1e3fbb49ca1b00ef0c.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563