I've just installed quexf and I'm trying to get it run with the example form test_blank.pdf given in the doc dir. The problem is that I select the correct file with the right description in "Import a new form from a PDF file" section, but when I click on the Submit button the result page is blank.

So I've checked error.log and got the following error:
PHP Fatal error:  Call to undefined function imagecreatefromstring() in /var/www/quexf/functions/functions.import.php on line 170, referer: http://localhost/quexf/admin/new.php

I've put some debug row into /var/www/quexf/functions/functions.import.php to check if there are some problems with the imported file, but everything seems ok.

If I put a print statement after the line:

$image = imagecreatefromstring($data);

nothing is shown.

I don't understand where could be the problem, is that due to an uncorrect installation?

Could someone help me please in making it work.

Thanks in advance.