How to edit images (remove background) in InDesign?

Hi, I'm writing a book and using InDesign which is great, and Adobe images that I've bought look great - but I wanted to add a few sketches that I've done myself - pen on white paper, scanned on my HP printer on High at 600dpi - you can see little off white on the InDesign screen, but when I export to PDF to review it looks a lot worse - any ideas on how I can get the background whiter?  Many thanks, Paul B

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