Как в libcurl отправлять картинку методом post?

string as_curl::exec()
{
        //cout << disBodyFlag;
        //return "";
        buffer.clear();
 
    curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, errorBuffer);
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
    curl_easy_setopt(curl, CURLOPT_HEADER, header);
    curl_easy_setopt(curl, CURLOPT_PROXYTYPE, CURLPROXY_HTTP);
    //curl_easy_setopt(curl, CURLOPT_PROXYPORT, port);
    curl_easy_setopt(curl, CURLOPT_PROXY, proxy.c_str());
//curl_easy_setopt(curl, CURLOPT_PROXY, "190.144.127.202:3128");
 
    curl_easy_setopt(curl, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1");
 
#ifdef SKIP_PEER_VERIFICATION
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
#endif
 
#ifdef SKIP_HOSTNAME_VERFICATION
     curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
#endif
 
    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, followFlag);
    curl_easy_setopt(curl, CURLOPT_REFERER, referer.c_str());
 
    curl_easy_setopt(curl, CURLOPT_NOBODY, disBodyFlag);
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writer);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &buffer);
    qApp->processEvents();
        if(postdata != "")
        {
                curl_easy_setopt(curl, CURLOPT_HTTPPOST, 1);
                curl_easy_setopt(curl, CURLOPT_POSTFIELDS, postdata.c_str());
                curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, postdata.length());
                qApp->processEvents();
        }
 
        curl_easy_setopt(curl, CURLOPT_COOKIE, cookie.c_str());
    result = curl_easy_perform(curl);