Cloud.users.update photo returns success but no change, wrong media type?

In my MebileWeb, WebView I browse to the image using

<input type="file" id="files" name="files[]" multiple />
<output id="list"></output>

then I extract and confirm the file with

<script>
function handleFileSelect(evt) {
    var files = evt.target.files; // FileList object
 
    for (var i = 0, f; f = files[i]; i++) {
        if (!f.type.match('image.*')) {
            continue;
        }
        var reader = new FileReader();
        // Closure to capture the file information.
        reader.onload = ( function(theFile)
        {
            return function(e) {
            // test thumbnail
            var span = document.createElement('span');
            span.innerHTML = ['<img class="thumb" src="', e.target.result, '" title="', escape(theFile.name), '"/>'].join('');
            document.getElementById('list').insertBefore(span, null);
        };
     })(f);
 
      reader.readAsDataURL(f);
    }
}
 
  document.getElementById('files').addEventListener('change', handleFileSelect, false);
</script>

and finally, update the logged-in user, (which does not yet have a photo), with reader.onload's e.target.result

// { result : e.target.result } is passed from WebView's HTML reader.onload to this external .js
Cloud.Users.update({
    photo: e.result
    }, function (e) {
        if (e.success) {
            var u = e.users[0];
                        var S = 'user :';
            for (i in u) {
                S += '\n'+i+':'+u[i];
                if (i === 'photo') {
                    S += '\n'+i+':'+u[i].urls.original;
                }
            }
            alert(S); 
    } else {
        alert('Error: ' + ((e.error && e.message) || JSON.stringify(e)));
    }
});

The result is success but does not update the image. I am guessing that I am not passing the correct format to the cloud with readAsDataURL