Uploading an image from android to google app engine?

I'm trying to take a photo on an android app, and then send it to my google app engine app.

I have the taking a photo part done, however I'm struggling with the rest.

This is what I'm using the send the image:

// send to AppEngine
                // the view you want to create as an image
                var saveImageView = Titanium.UI.createImageView({
                    top : 0,
                    left : 0,
                    width : 'auto',
                    height : 'auto',
                    image : event.media,
                });
 
                win1.add(saveImageView);
                imageToUpload = saveImageView.toBlob();
                // toBlob, not toImage!! important...
                var xhr = Titanium.Network.createHTTPClient();
                xhr.onload = function() {
                    win1.remove(saveImageView);
                    // remove the temp view...
                };
                xhr.open('POST', '???');
                xhr.send({
                    image : imageToUpload
                });
                /////////////////////

I know it's got to be the address to my GAE app's server (at least I think), but I'm not sure how to find this address, nor how to setup my GAE app to make uploading the image possible like this.

Any help would be greatly appreciated.