I use an NGINX web server on my Ubuntu server and I kept getting HTTP Error when uploading images.
These links helped me fix it:
https://wordimpress.com/wordpress-nginx-http-error-on-image-uploader-fix/#comment-57740
https://wordpress.org/support/topic/http-error-on-image-uploader-1/
I had to edit:
/etc/nginx/nginx.conf
and add
client_max_body_size 100m;
to the http{} section.
I reloaded nginx with
sudo systemctl reload nginx
and the error went away.