There are several possibilities here so a couple of guesses:

If the images are severely pixelated, perhaps you're using some kind of image field which creates thumbnails and you're using the thumbnail instead of the image?

If the images are somewhat pixelated, perhaps you've set the quality too low when resizing? Perhaps you should enable antialiasing?

If the images are only very slightly pixelated, you might want to compare using imagemagick instead of Pillow or similar. My experience is that imagemagick produces slightly better images when resizing and thumbnailing but I also think the difference has become smaller and smaller over the years. I used to use imagemagick for this reason but I don't anymore.

Let me know how you process image uploads in Django and I can likely come up with a better answer.

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