Droplet is an AJAX uploader supporting drag-and-drop, with a progress bar and an image resizer. It's known to be compatible with Firefox and Chrome, and possibly other browsers.

To use, add the javascript and CSS in the page, then set Droplet.form to your upload form (the form is used as a fallback if Droplet is incompatible, and other form widgets can also be used), and Droplet.zones to an array of elements that will accept dropped files:

Droplet.form = document.getElementById('form');
// this line isn't needed if the whole page should accept dropped files
Droplet.zones = [document.getElementById('zone')];

To do something on completion of upload, set an uploadComplete callback:

Droplet.uploadComplete = function (req) {
	document.getElementById('output').textContent = req.responseText;
};

Droplet can reduce PNG or JPEG files before upload to save upload time. To use this feature, set a maximum width and height for images. If you set a threshold, images won't be scaled if the size of the reduction is greater than the threshold (in this case if they're already smaller than 800/0.9=889px).

Droplet.maxWidth = Droplet.maxHeight = 800;
Droplet.threshold = 0.9; // default is 1.0

Droplet can also encode JPEG at different qualities to further reduce upload time (this is not supported in all browsers).

Droplet.quality = 0.5; // between 0.0 and 1.0, default is 0.8