Invoice Ninja - "There was a problem reading the image file, please try a different format." [missing dependency]

[JedMeister]

As reported by Lee in the forums the v16.0 Invoice Ninja appliance errors when you try to upload an image; with the message "There was a problem reading the image file, please try a different format.". As I noted in my response, it appears to be a missing dependency, namely the php-gd package.

As I went on to note in my response, I think that there are actually some other missing dependencies.

To install all the (suspected) missing dependencies (as root; otherwise prefix each line with sudo):

apt update
apt install php-gd php-xml php-mbstring
systemctl restart apache2