javascript - Reading image capture files in PhoneGap

I'm working on a PhoneGap application that captures images using the camera and, later, uploads them. There are two modes of operation for camera in PhoneGap: raw base64 encoded data or a file URI.

The docs themselves say:

Note: The image quality of pictures taken using the camera on newer
devices is quite good. Encoding such images using Base64 has caused
memory issues on some of these devices (iPhone 4, BlackBerry Torch
9800). Therefore, using FILE_URI as the 'Camera.destinationType' is
highly recommended.

So I'm keen to use FILE_URI option. This works great and you can even show the images in IMG tags. The URL looks like this:

file://localhost/var/mobile/Applications/4FE4642B-944C-449BB-9BD6-1E442E47C7CE/tmp/photo_047.jpg

However, at some point later I want to read the contents of the file to upload to a server. I was going to do this using the FileReader type. This doesn't work and I think it's because I can't access the file at the URL above.

The error code I get back from readDataUrl is 1 > FileError.NOT_FOUND_ERR = 1;

Any ideas how I can get to the file? I tried just accessing the last part of the path (photo_047.jpg) based on another sample I saw but no luck.