Captcha image not showing using php-7

Here my problem and solution for me.

Because joomla encourage you to use php-7 I think this is a problem more people can get.

In the version with php-5 all was okee. After switching to php-7 the captcha-image did not show.

First I could not find the solution. On my live site Captcha image shows in php5 and not in php7. I put my site local with XAMP with php7 and it workt. So it has to be something with the php on my server. So I google for captcha image not showing and read about the GD libary.

I did not realise that for every php version you have to install the GD libery.
On my server I installed php but without GD.

Installing GD fot php7 did the trick.

Have a nice day!

Rolf