The best thing to do would be to adjust the QuickFile invoice layout to update it to suit your setup rather than put a JPG behind it.
If you have any experience with CSS, then you can tweak it by previewing an invoice, clicking the green “Invoice Style Gallery” (top left) and picking a template. Then clicking “Customise this style” to adjust it as needed.
This guide may also help: 10 basic CSS tricks for styling your invoices
Of course, if you’re stuck, please let us know and we’ll try our best to help 