tx.js

document.getElementById('file').addEventListener('change', readFile, false);

function readFile(evt) {
    var files = evt.target.files;
    var file = files[0];
    var reader = new FileReader();

    reader.onload = function (event) {
        var binaryString =  btoa(event.target.result);
        TXTextControl.images.addInline(binaryString, -1);
    }

    reader.readAsBinaryString(file);
}