Printing an image onto the PDF will maintain with the rectangular height and width of the image.
You might have a scanned image which covers areas that you don’t want included and want to insert the image without the rectangular shape.
Images with the alpha channel removed (masked) makes the removed sections transparent so only the image you want is inserted. This is done with photo editing software.
Once you have the masked image as desired, use the SetHeaderImage method in Toolkit as the means to overlay the image onto the PDF.