It might also be set-up to save your screenshots as a .jpg. If you change it to save as a .bmp, the filesize will be much larger, and will be much clearer.
When you save as a .jpg, the original image gets compressed to save filesize. So it loses image quality and looks fuzzy. Saving your screenshots as a .bmp keeps it as a large high-quality image, and it'll look crisp and nice.
In Modelviewer at the top of the screen, click on Settings, then Screenshot Formats, and make sure it's saved as a .bmp.