The best quality would be to get the images directly from the SD card in the drone.
You can download them to the phone/device for a better image than you posted, however, by hitting the little "download" icon when previewing the image in the app... What you posted looks like a thumbnail from the very small and low resolution "cache" file that is saved to the phone by default.
You have to retrieve/view the images from the DJI app's folder on the phone for the better images if they were downloaded correctly. The higher quality images will be highlighted/checked as "original".
That looks like a cache image. Spark saves cache images and videos to your device. If you have a way to transfer files straight from the SD card you'll have better images. You should have pics like this