The bare minimum code to upload an image file to the StoreScaledImage.groovy script

BareBonesImageUpload.js

var PLATFORM_HOST = document.URL.split('/apps/')[0]; // this is how you would retrieve the host on an Axeda instance

var SESSION_ID = null // usually retrieved from login function included below

/***
 * Depends on jQuery 1.7+ and HTML5, assumes an HTML5 element such as the following:
 * <input type="file" id="fileinput" value="Upload" />
 * **/

$("#fileinput").off("click.filein").on("click.filein", function () {
    fileUpload()
})

var fileUpload = function () {
    $("#fileinput").off('change.fileinput')
    $("#fileinput").on('change.fileinput', function (event) {
        if (this.files && this.files.length > 0) {
            handleFiles("http://" + PLATFORM_HOST, this.files)
        }
    })
}

var handleFiles = function (host, files) {
    $.each(files, function (index, file) {
        var formData = new FormData();
        var filename = file.name
        formData.append(filename, file)
        var url = host + '/services/v1/rest/Scripto/execute/StoreScaledImage?filelabel=' + filename + "&tag=myimg"

        url = setSessionId(url)
        jQuery.ajax(url, {
            beforeSend: function (xhr) {
                xhr.setRequestHeader('Content-Disposition', filename);
            },
            cache: false,
            cache: false,
            processData: false,
            type: 'POST',
            contentType: false,
            data: formData,
            success: function (json) {
                refreshPage(json)
                console.log(json)
            }
        });
    })
}

var setSessionId = function (url) {
    // you would already have this from logging in
    return url + "&sessionid=" + SESSION_ID
}

var refreshPage = function (json) {
    // here you would refresh your page with the returned JSON   
    return
}

/***
 *  The following functions are not used in this demonstration, however they are necessary for a complete app and are found in axeda.js  http://gist.github.com/axeda/4340789
 ***/

    function login(username, password, success, failure) {
        var reqUrl = host + SERVICES_PATH + 'Auth/login';
        localStorage.clear()
        return $.get(reqUrl, {
            'principal.username': username,
                'password': password
        }, function (xml) {
            var sessionId = $(xml).find("ns1\\:sessionId, sessionId").text()
            // var sessionId = $(xml).find("[nodeName='ns1:sessionId']").text(); - no longer works past jquery 1.7
            if (sessionId) {
                // set the username and password vars for future logins.           
                storeSession(sessionId);
                success(SESSION_ID); // return the freshly stored contents of SESSION_ID
            } else {
                failure($(xml).find("faultstring").text());
            }
        }).error(function () {
            $('#loginerror').html('Login Failed, please try again')
        });
    };

function storeSession(sessionId) {
    var date = new Date();
    date.setTime(date.getTime() + SESSION_EXPIRATION);
    SESSION_ID = sessionId
    document.cookie = APP_NAME + '_sessionId=' + SESSION_ID + '; expires=' + date.toGMTString() + '; path=/';
    return true;
};