(Why?) Image size nearly doubles when uploading to S3 - Django

When I upload an image via Django to Amazon's S3, the image size nearly doubles. For example, I upload an image to Django that is 17.4KB, but when I look at my S3 bucket, the image is 33.2KB.

Is there a reason why this is happening? Below are my forms and views to see the processes. I can't seem to figure out why this is happening.

forms.py:

class PhotoUploadForm(forms.ModelForm):
    class Meta:
        model = Photo
        fields = ('photo',)

views.py:

@login_required
def photo_upload(request):
    form = PhotoUploadForm(request.POST or None,
                           request.FILES or None,
                           request=request)

    if request.method == 'POST':
        if form.is_valid():
            obj = form.save(commit=False)
            obj.creator = request.user
            obj.slug = get_random_string(length=10)
            obj.save()
            return HttpResponseRedirect(reverse('home'))
    return render(request, 'photos/photo_upload.html', {'form': form})

Thank you in advance for any help!