Can't you adjust the contrast and lightness/darkness of the receipt before you attach it to your report?
Like others have noted, I adjust these when I scan. My scanner tends to scan light, so I have it permanently adjusted to a darker setting and higher contrast so that these faint receipts come out legible.
If you photograph your receipts instead of scanning, you can use a photo program to enhance the image before sending it.
I learn something new every day, but not everyday!
I've learned to never trust spell-check or my phone's auto-fill feature.