void MainWindow::uploadScreenshotToServer(QUrl uploadUrl)
{
    QFile file("img.png");
    if(file.open(QIODevice::ReadOnly)) {

        QNetworkRequest request;
        request.setUrl(uploadUrl);
        request.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("application/x-www-form-urlencoded"));
        QByteArray boundary("56gfqgE8VdoO");
        QByteArray data;

        data.append("Content-Type: multipart/form-data; boundary=");
        data.append(boundary);
        data.append("\n\n--");
        data.append(boundary);
        data.append("\n");
        data.append("Content-Disposition: form-data; name=\"photo\"; filename=\"img.png\"\n");
        data.append("Content-Type: image/png\r\n");
        data.append("Content-Transfer-Encoding: binary\n\n");
        data.append(file.readAll());
        data.append("\n--");
        data.append(boundary);
        data.append("--\n");

        reply = manager.post(request, data);
        connect(reply, SIGNAL(finished()), this, SLOT(uploadScreenshotToServerReplyFinished()));
    }
    file.close();
}

{
    QFile file("img.png");
    if(file.open(QIODevice::ReadOnly)) {
        QNetworkRequest request;
        request.setUrl(uploadUrl);

        QHttpMultiPart multiPart(QHttpMultiPart::FormDataType);
        QHttpPart imagePart;
        imagePart.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("image/png"));
        imagePart.setHeader(QNetworkRequest::ContentDispositionHeader, QVariant("form-data; name=\"photo\""));
        imagePart.setBodyDevice(&file);

        multiPart.append(imagePart);

        reply = manager.post(request, &multiPart);
        connect(reply, SIGNAL(finished()), this, SLOT(uploadScreenshotToServerReplyFinished()));
    }
    file.close();
}