After installing Ghost, I discovered that I couldn't upload images larger than 1 MB. The problem is not with Ghost itself but with a configuration setting on the reverse proxy Nginx.
To fix this, edit nginx.conf.
sudo nano /etc/nginx/nginx.conf
Add this line to the http
section.
client_max_body_size 5m;
I chose 5 MB but you can choose whatever you feel is appropriate for your environment. Setting it to 0
disables the limit.
Then...
sudo service nginx stop
sudo service nginx start
Done!