You noticed that user thumbnails in SharePoint 2013 are unclear or blurry? Particularly evident when viewing My Site Host’s People page (MyPeople.aspx). The user images on the left are of bad quality. This is because Microsoft changed the default thumbnail sizes.
The new dimensions for the medium and small images arent’t much of a problem thanks to this PowerShell cmdlet
Update-SPProfilePhotoStore -MySiteHostLocation http://mysites
Read more at TechNet. By executing this script thumbnail images are regenerated within the thumbnail library to match the new default sizes.
One “problem”: The larger thumbnails will stay at a maximum 144 pixels. Since they are displayed at 200 pixels, the image will be slightly unclear or blurry. Unless you have a repository of larger images, there’s no answer.