What software would I need to create a website that others...anyone...can upload photos to?

When you say "anyone" are you talking about people you've previously approved or the general public?

I'd be wary of letting anyone upload pictures to your web site, at least unless you're willing to moderate said pics. You're likely to find yourself with some unusual spam.

Easiest way to handle uploads would be to install a bulletin board that allows for file uploads. Some of them (most of them?) have an option to allow uploads. This option can be turned on or off -- most web masters seem to turn that option "off" for bandwidth and security reasons.

Most bulletin boards are pretty easy to upload and install. Ask your ISP if you're allowed to.

Note that if you allow for file uploads you WILL want to keep on top of security updates for whatever bulletin board you pick. Pick a popular one that gets frequent updates. Allowing for file uploads means a certain amount of security risk.