We can change the resolution the images on a link content type by editing the settings of the content. To do this we can do this from School Website > Content > Additional Content Types > Links > Edit any content from the gear option. At the bottom, we can change the max resolution. If it is too small stretching it will cause the blurriness and artifacts. This can also be an artifact of the way that the JPEG file format compresses images. If possible, try to upload a PNG in place of the JPEG.