Image quality

Currently if I upload an image URL from the web, its 60x60 thumbnails are reasonably good quality.  But if I download that image to my PC and then upload it to a different image field in Knack, the thumbnails are much lower quality.  It acts as if the image quality is reduced on the "way up" (uploading).  Does anyone know if that is the case and/or if there is a workaround?