Good try. Not sure what to do.
Here is a Uruguay stamp scanned at 600 and then cropped and reduced to 75% in my editing program.

At 1200 you should see the lint in her belly button.
Perhaps it is the cropping tool or reducing program you are using. Are you reducing the actual size in pixels of the photo or just the percentage of the whole picture down to a smaller percentage? Confusing to say, sorry.
Or, maybe the stamps are just that way. I do not have any here to compare unfortunately.