Facebook is the largest photo sharing service in the world, with over 2 billion photos uploaded by users each month. So when the company is testing a brand new way for users to get most of those photos onto the site, it’s a big change.

Although the current photo uploading tools are obviously working well enough to support the current volume of photo sharing on Facebook, many users have some technical problems when uploading photos. As a result, Facebook has decided to forego relying upon ActiveX controls, Java applets, and even Flash in a new version of the photo uploader tool it’s testing. Instead, it’s built entirely in JavaScript, CSS, and HTML. Users can test the new uploader by activating the “prototype” app.

When you activate the new photo uploader, here’s how it looks:

Here’s how it works, according to Facebook’s Chris Putnam,

The photos in thumbnail view are served by a light-weight local web server thread, while the filesystem information is provided through a JavaScript API. After selecting photos and starting an upload, you’ll discover another great feature–asynchronous uploading. The plug-in spins off a background thread to perform the upload regardless of what the browser is doing in the foreground. Then the local web server provides JSONP endpoints to retrieve progress information or cancel the ongoing upload, without needing to re-embed the plug-in itself. With this approach you can even navigate away from Facebook entirely without worrying about your uploads.

Facebook goes into detail on its approach to the security model in the new uploader here.

Obviously, maintaining security around user data is a primary concern for Facebook, so the team behind the new photo uploader is going to be doing a lot of testing and observing to see how the new tool is used. “Depending on the results of these tests, we hope to roll it out to all users soon,” Putnam says.