Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/50c5b564075f18f48bb977e5d937a11d.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563