If not, store it on your database as blobs.

Regardless on which one above you choose, if you implement something like Cloudflare, you can get a CDN for those images. If you don't want everything behind Cloudflare, you can have the images served under a different subdomain and have that under cloudflare.

If not, an alternative to S3 is Google Cloud Storage. Create a bucket. Set it as public (everything in the bucket is available) and then you just need to worry about upload.

Here's a quick example in python, https://pypi.org/project/google-cloud-storage/

    bucket = client.get_bucket('bucket-id')
    new_blob = bucket.blob('remote/path/storage.txt')
    new_blob.upload_from_filename(filename='/local/path.txt')
    # or
    blob.upload_from_string('New contents!')