To post data use ASIFormDataRequest
NSURL *url = [NSURL URLWithString:@"http://test.com/misc/app/ws/ws_user_registration.php?"];
ASIFormDataRequest* asiRequest = [ASIFormDataRequest requestWithURL: url];
[asiRequest setPostFormat:ASIMultipartFormDataPostFormat];
[asiRequest addData:DATA_TO_SEND withFileName:FILE_NAME andContentType:FILE_CONTENT_TYPE forKey:YOUR_FILE_UPLOADKEY;
[asiRequest setDidFinishSelector:@selector(connectionFinishedLoading:)];// called when connection successfully got finished and recieve resoponse
[asiRequest setDidFailSelector:@selector(requestWentWrong:)]; // called when connection went wrong due to bad url connection or timeout, etc.
[asiRequest setDelegate:self];
[asiRequest startAsynchronous];
For more info read asihttp docs