Captcha not working on CentOS 7 after ImageMagick upgrade

We have an issue in CentOS with latest GD::Image and ImageMagick modules, the captcha size is always one character:

[root@kptn-centos7 ~]# rpm -qa | grep -i magic
ImageMagick-6.7.8.9-18.el7.x86_64
perl-Variable-Magic-0.54-2.el7.x86_64
ImageMagick-perl-6.7.8.9-18.el7.x86_64

I don't have this issue on Ubuntu, with these versions:

root@llng-site:~# dpkg -l | grep -i magick
ii  imagemagick-6-common                       8:6.9.7.4+dfsg-11+deb9u7                     all          image manipulation programs -- infrastructure
ii  libimage-magick-perl                       8:6.9.7.4+dfsg-11+deb9u7                     all          Perl interface to the ImageMagick graphics routines
ii  libimage-magick-q16-perl                   8:6.9.7.4+dfsg-11+deb9u7                     amd64        Perl interface to the ImageMagick graphics routines -- Q16 version
ii  libmagickcore-6.q16-3:amd64                8:6.9.7.4+dfsg-11+deb9u7                     amd64        low-level image manipulation library -- quantum depth Q16
ii  libmagickwand-6.q16-3:amd64                8:6.9.7.4+dfsg-11+deb9u7                     amd64        image manipulation library -- quantum depth Q16
ii  php-imagick

A workaround is to disable ImageMagick for Captcha :

diff --git a/lemonldap-ng-portal/lib/Lemonldap/NG/Portal/Lib/Captcha.pm b/lemonldap-ng-portal/lib/Lemonldap/NG/Portal/Lib/Captcha.pm
index c4ee4ee1b..5304528b8 100644
--- a/lemonldap-ng-portal/lib/Lemonldap/NG/Portal/Lib/Captcha.pm
+++ b/lemonldap-ng-portal/lib/Lemonldap/NG/Portal/Lib/Captcha.pm
@@ -1,7 +1,7 @@
 package Lemonldap::NG::Portal::Lib::Captcha;
 
 use strict;
-use GD::SecurityImage use_magick => 1;
+use GD::SecurityImage use_magick => 0;
 use Mouse;
 use MIME::Base64;

But the result is not as good as with ImageMagick.