I'm not entirely sure but I think converting the image to a vector file should do the trick.
I don't know any sites that do it off hand but I'm sure you can Google it.
I don't know why , but when using these guys from fiverr they manage to get you amazing prices, but sometimes or rather lately the USPS lables are always blurry, try to ask them to resend it and do this and that it doesn't help.
Don't know what they're doing, if there so good in copy pasting and making barcodes at least they should perfect the quality and pixels of the label, they look amazing if it was in fact a fake but why kill the resolution? And the lables I always bring inside the post office to verify its a legit label and will actually work.
I know myself I can get some crazy pricing on FedEx overnight as I'm connected with a huge account, but curios how every tom and Harry has a USPS account that can make profit selling for $5?
Aside for this asking for pictures as well.