HP print drivers are a pain for this, particularly if you enlarge the image.
It is most noticeable in word/excel when someone prints at say 110% but I have seen it in VFP too. Try updating the print drivers, it is more common on older printers or older parallel ported deskjets (the usb drivers seem more reliable but there are times when you can't use the usb versions).
Regards
Michael Hawksworth