Marble displays map unsharp. It looks like the marble choose wrong zoom level tiles from OSM server.
Compare this 2 links:
1. How map is displayed in Marble:
And how it should looks like (screenshot from browser):
Steps to Reproduce:
1. Run marble
Thanks for the bug report. This behavior / view is intentional. You can get a sharp display however when choosing "Merkartor" as projection and zoom using the +/- keys or the +/- buttons in the Navigation tab.
*** This bug has been marked as a duplicate of bug 199259 ***