How to sort pictures by name

this works :http://ndlc.info/program
these don't work:
http://ndlc.info/program/sessions
http://ndlc.info/program/collection-and-access
http://ndlc.info/program/Programming-Outreach-and-Advocacy
http://ndlc.info/program/challenging-topics
http://ndlc.info/program/posters
http://ndlc.info/program/personnel-management-and-organization

I just think the problem is that you are not explicitly setting the order. When you don't set an order, it's just going to use the order as defined in the filesystem. This is going to be different depending on the server and OS, and is very unreliable.

I would suggest setting the order with folder, ascending, something like this:

title: "PROGRAM"
body_class: posters
published: true
visible: false
template: sessions
content:
    items:
        '@taxonomy.category': session
        '@page': '/program/sessions'
    order:
        by: folder
        dir: asc

Full details on the ordering options are in the docs

NOTE: You will hae to set this order on every page that has a content collection defined in the page header.

Thank you! I will try that.