Thank you for writing us back.
We have logged the feature request in our system with ID BARCODENET-36572. Our product team will further look into it and provide feedback. We will update you with the feedback in the forum thread once available.
For now you may try the following code snippet as work around.
using (BarCodeBuilder builder = new BarCodeBuilder("123456789012", EncodeTypes.EAN13))
using (Bitmap barcode = builder.GenerateBarCodeImage())
using (Bitmap picture = (Bitmap)Image.FromFile(@"path_to_your_picture.png"))
using (Bitmap output = new Bitmap(Math.Max(barcode.Width, picture.Width), barcode.Height + picture.Height))
using (Graphics g = Graphics.FromImage(output))
g.DrawImage(picture, new PointF(0, 0));
g.DrawImage(barcode, new PointF(0, picture.Height));