After discussing with the developer I found that we can't support extraction of image at a specified location. What you can do that if you know the page number on which that Barcode image is present in the Pdf then Extract the images, but here specifically defining an image to extract is not supported. Here is a piece of code that can extract image from a specified page by setting Start and End page properties of PdfExtractor class.
PdfExtractor extractor = new PdfExtractor();
extractor.StartPage = 1;
extractor.EndPage = 2;
String prefix = @"D:\Test\Image";
String suffix = ".jpg";
int imageCount = 1;
extractor.GetNextImage(prefix + imageCount + suffix);
If you need more help, please do let us know.