Default sorting of photos

FooGallery offers many different album settings:

• Default
• Date created – newest first
• Date created – oldest first
• Date modified – most recent first
• Date modified – most recent last
• Title – alphabetically
• Title – reverse
• Random

None of them is “Filename”, though. Or is that what “Default” does?

Could someone explain what the default sorting is — and, if it’s not by filename, how we can achieve that, or if it can be added as an option?

-Ken