The concept of determining a URL or Image Directory based on a file location on a server is very important, but not very intuitive to most people. You may need to read this section multiple times.

When you enter a URL into a browser, how does the web server know where the file is? It typically starts looking in the root of the website, which is usually specified by the web server administrator. When you go to the Allsky WebUI, for example via http://allsky, Allsky looks in ~/allsky/html since that's what the Allsky developers specified as the root of the WebUI.

There are two paths to a web file - one via a URL and another via the filesystem on the server. The web server maps a URL to a file location on the server. In our example above your Pi mapped http://allsky to ~/allsky/html. Sometimes that mapping is easy, and other times it's more difficult. In both cases, it impacts what you enter into the Image Directory setting for the remote Website or Server.

The cases below assume you want to send your allsky images to a remote Allsky Website but the same thing applies if you want to send the allsky images to remote server that is not an Allsky Website.

Easy case: server directory structure matches URL

Let's say you have a personal website at https://mysite.com where you store family photos. When you access the server (usually via FTP) you see the family photos without having to navigate anywhere. This means your website URL maps to the top-most directory of the remote server's directory structure, called the "root" directory.

To use that server as an Allsky Website you create a directory in the root of the server called allsky and install an Allsky Website there. (Visit the Allsky Website Installation page to see how).

The URL to your remote Allsky Website would be https://mysite.com/allsky. In the WebUI you'd set the Remote Server's Image Directory to /allsky (or allsky depending on your service provider).

More difficult case: directory structure does not match URL

You have the same website URL as above, but when you access the remote server you don't see the photos; instead, you see a directory called public_html (the actual directory(s) you see will depend on your service provider). When you go into the public_html directory you see your photos.

In this case the web server is mapping the https://mysite.com URL to your /public_html directory. You need to create a /public_html/allsky directory on the server and install the Allsky Website there. The URL to the Allsky Website is still https://mysite.com/allsky but in the WebUI you'd set the Remote Server's Image Directory to /public_html/allsky (or public_html/allsky depending on your service provider).

Mapping URLs to server directories like this is fairly common on remote servers that are shared by many people.