How can we upload background file to iphone?

You can do it this way (it's mostly cut and pasted from one of my projects). Credit goes to some position on development forums, but I don't know who it was from:

- (IBAction)startUpload:(id)sender {
    NSString *filename = [NSString stringWithFormat:@"iphone-%d.png", [NSDate timeIntervalSinceReferenceDate]];

    NSString *boundary = @"----BOUNDARY_IS_I";

    NSURL *url = [NSURL URLWithString:@"http://yourgreatwebsite.com/upload"];

    NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];

    [req setHTTPMethod:@"POST"];

    NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@", boundary];

    [req setValue:contentType forHTTPHeaderField:@"Content-type"];

    NSData *imageData = UIImagePNGRepresentation([imageView image]);

    // adding the body
    NSMutableData *postBody = [NSMutableData data];


    // first parameter an image
    [postBody appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
    [postBody appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"filename\"; filename=\"%@\"\r\n", filename] dataUsingEncoding:NSUTF8StringEncoding]];
    [postBody appendData:[@"Content-Type: image/png\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
    [postBody appendData:imageData];

    // second parameter information
    [postBody appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
    //[postBody appendData:[@"Content-Disposition: form-data; name=\"some_other_name\"\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
    //[postBody appendData:[@"some_other_value" dataUsingEncoding:NSUTF8StringEncoding]];
    //[postBody appendData:[[NSString stringWithFormat:@"\r\n--%@--\r \n",boundary] dataUsingEncoding:NSUTF8StringEncoding]];

    [req setHTTPBody:postBody];

    //start the spinner and deactivate the buttons...
    [self setButtonsEnabled:NO];


    [[NSURLConnection alloc] initWithRequest:req delegate:self];
  }

  #pragma mark urlconnection delegate methods
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // this method is called when the server has determined that it
    // has enough information to create the NSURLResponse

    // it can be called multiple times, for example in the case of a
    // redirect, so each time we reset the data.
    // receivedData is declared as a method instance elsewhere
    [receivedData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // append the new data to the receivedData
    // receivedData is declared as a method instance elsewhere
    [receivedData appendData:data];
}

- (void)connection:(NSURLConnection *)connection
  didFailWithError:(NSError *)error
{
    // release the connection, and the data object
    [connection release];

    // inform the user
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Upload Error" message:[NSString stringWithFormat:@"The upload failed with this error: %@", [error localizedDescription]] delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
    [alert release];

    NSLog(@"Connection failed! Error - %@ %@",
          [error localizedDescription],
          [[error userInfo] objectForKey:NSErrorFailingURLStringKey]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // do something with the data
    // receivedData is declared as a method instance elsewhere
#ifdef DEBUG
    NSLog(@"upload succeeded!");
#endif

    // release the connection, and the data object
    [connection release];

    NSString *response = [NSString stringWithCString:[receivedData bytes] length:[receivedData length]];    


#ifdef DEBUG
    NSLog(response);
#endif
}