QNetworkAccessManager: disable cache for concrete document

Hi,
I don't want to cache concrete image on website page (using many qwebview for one site). For this I overload QNetworkAccessManager's method createRequest(), make condition for my image (if (myReq.url() == myUrl) then not apply
cache), and try in this condition:
1) myReq.setRawHeader( new QByteArray("Cache-Control"), new QByteArray("no-cache") ); //not work
2) myReq.setRawHeader( new QByteArray("If-Modified-Since""), new QByteArray(myTime) ); //not work
3) myReq.setUrl(new QUrl(url2 + "&x=" + rand.nextInt(1000000))); //not work too, url becomes really other, but however image in cache.

How I must abolish cash for document (in my case - image)? Thanks.
p.s. sorry for my english

Probably I explained badly.
There is a lot of threads, each of them using QWebView. Also we have one url for each of them.
Task: to compel createRequest (method of QNetworkAccessManager) to take a resource (in my case it is gif-image on website) from the network, instead of from cache.

Some code of one thread:

Code:

---

this.webPage.page().setNetworkAccessManager(new CorrectNetworkAccessManager(this.ip, this.port));
 this.webPage.load(this.url);

---

Code of class CorrectNetworkAccessManager (which extends QNetworkAccessManager):

Code:

---

class CorrectNetworkAccessManager extends QNetworkAccessManager
{
  int _port;
  String _ip, userAgent, acceptLanguage, acceptCharset;
 
  public CorrectNetworkAccessManager(String ip, int port)
  {
   this._ip   = ip;
   this._port = port;
  }
 
  @Override
  protected QNetworkReply createRequest(Operation op, QNetworkRequest request, QIODevice outgoingData)
  {
   QNetworkRequest myReq = new QNetworkRequest(request);
 
   /*This show url of each resource of webpage. If number of threads is 10 and webpage contains, for example, gif-image 
(<img src="myimage.gif">), this method show us only ONE gif-image url, and it is necessary to do, that 10 showed. I.e. 
to abolish cache for this picture. However, if webpage contains php-page, it show 10 times! (because php-page not 
caching) */ 
   System.out.println(myReq.url());
 
   this.userAgent = "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/532.0 (KHTML, like Gecko)";
   this.acceptLanguage = "ru-RU,ru;q=0.8,en-US;q=0.6,en;q=0.4";
   this.acceptCharset = "windows-1251,utf-8;q=0.7,*;q=0.3";
 
   myReq.setRawHeader( new QByteArray("User-Agent"), new QByteArray(this.userAgent) );
   myReq.setRawHeader( new QByteArray("Accept-Charset"), new QByteArray(this.acceptCharset) );
   myReq.setRawHeader( new QByteArray("Accept-Language"), new QByteArray(this.acceptLanguage) );
 }
}

---

How to abolish cach for image? Thanks for answers.