Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/20b786f5bf9172869f38d3bf222e63d3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563