In fact we need the gsfonts package to draw CAPTCHA instead of ghostscript (it was my mistake).
Also I added captcha_cmd parameter to configuration file template. If EJABBERD_CAPTCHA environment var value is true, captcha_cmd will set to EJABBERD_CAPTCHA_CMD with fallback to /usr/local/lib/ejabberd-18.04/priv/bin/captcha.sh.
In fact we need the
gsfontspackage to draw CAPTCHA instead ofghostscript(it was my mistake). Also I addedcaptcha_cmdparameter to configuration file template. IfEJABBERD_CAPTCHAenvironment var value istrue,captcha_cmdwill set toEJABBERD_CAPTCHA_CMDwith fallback to/usr/local/lib/ejabberd-18.04/priv/bin/captcha.sh.