Script to convert image into base64, using xhr2 without canvas. Therefore it is possible to convert images from another domains, using CORS.

getBase64FromImage.js

function getBase64FromImage(url, onSuccess, onError) {
    var xhr = new XMLHttpRequest();
 
    xhr.responseType = "arraybuffer";
    xhr.open("GET", url);
 
    xhr.onload = function () {
        var base64, binary, bytes, mediaType;
 
        bytes = new Uint8Array(xhr.response);
        //NOTE String.fromCharCode.apply(String, ...
        //may cause "Maximum call stack size exceeded"
        binary = [].map.call(bytes, function (byte) {
            return String.fromCharCode(byte);
        }).join('');
        mediaType = xhr.getResponseHeader('content-type');
        base64 = [
            'data:',
            mediaType ? mediaType + ';':'',
            'base64,',
            btoa(binary)
        ].join('');
        onSuccess(base64);
    };
    xhr.onerror = onError;
    xhr.send();
}

not work for getting image from s3 amazon aws