I cut a region out of this Wikimedia Commons picture:
I simply used the free select tool to cut out the part (ctrl+x) and inserted it into another image without background.
However, when I export the project as PDF (File → Export as → Select file type → PDF), I get gray fringes around the border of the cut-out:
Why do these fringes appear? The image looks perfectly normal in GIMP, as shown in this picture:
Also in my default image viewer, when exported as PNG, the borders look perfectly normal:
Why do these fringes appear? Is there a way to remove them?