Q:

How to post an image in base64 encoding via .ajax?

I have some javascript code that uploads an image to a server. Below is the ajax call that works correctly.
$.ajax({
    url: 'https://api.projectoxford.ai/vision/v1/analyses?',
    type: 'POST',
    contentType: 'application/json',
    data: '{ "Url": "http://images.takungpao.com/2012/1115/20121115073901672.jpg" }',
})

I now need to upload the image a a base64 encoding e.g. 
data: 'data:image/jpeg;base64,/9j/4AAQSkZJRgA..........gAooooAKKKKACiiigD//Z'

But that doesn't work, i.e. the server doesn't recognise the data I send and complains.
Does anyone know what the correct format is for sending base64 encoded data in the AJAX call ?

A:

Thanks for all the answers which helped me along.
I had also posted the question to the forums on 
https://social.msdn.microsoft.com/Forums/en-US/807ee18d-45e5-410b-a339-c8dcb3bfa25b/testing-project-oxford-ocr-how-to-use-a-local-file-in-base64-for-example?forum=mlapi (more Project Oxford specific) and between their answers and your's I've got a solution.

You need to send a Blob
You need to set the processData:false and contentType: 'application/octet-stream' options in the .ajax call

So my solution looks like this
First a function to make the blob (This is copied verbatim from someone more gifted than I)
makeblob = function (dataURL) {
            var BASE64_MARKER = ';base64,';
            if (dataURL.indexOf(BASE64_MARKER) == -1) {
                var parts = dataURL.split(',');
                var contentType = parts[0].split(':')[1];
                var raw = decodeURIComponent(parts[1]);
                return new Blob([raw], { type: contentType });
            }
            var parts = dataURL.split(BASE64_MARKER);
            var contentType = parts[0].split(':')[1];
            var raw = window.atob(parts[1]);
            var rawLength = raw.length;

            var uInt8Array = new Uint8Array(rawLength);

            for (var i = 0; i < rawLength; ++i) {
                uInt8Array[i] = raw.charCodeAt(i);
            }

            return new Blob([uInt8Array], { type: contentType });
        }

and then
$.ajax({
    url: 'https://api.projectoxford.ai/vision/v1/ocr?' + $.param(params),
    type: 'POST',
    processData: false,
    contentType: 'application/octet-stream',
    data: makeblob('data:image/jpeg;base64,9j/4AAQSkZJRgA..........gAooooAKKKKACiiigD//Z'
 })
.done(function(data) {alert("success");})
.fail(function() {alert("error");});

A:

This is some working code from my own application.  You will need to change the contentType and data args in your ajax operations.
    var video = that.vars.video;
    var code = document.createElement("canvas");

    code.getContext('2d').drawImage(video, 0, 0, code.width, code.height);

    var img = document.createElement("img");
    img.src = code.toDataURL();    

    $.ajax({
        url: '/scan/submit',
        type: 'POST',
        data: { data: code.toDataURL(), userid: userid },
        success: function (data) {
            if (data.error) {
                alert(data.error);
                return;
            }
            // do something here.
        }, 
        error : function (r, s, e) {
                alert("Unexpected error:" + e);
                console.log(r);
                console.log(s);
                console.log(e);
            } 
        });

