 <p>Access to s3 can be secured in a variety of ways, but frequently people want to host these files directly out of s3, so they provide public access. You must have setup access to your bucket/objects so that they are public.</p> <p>You can also set the bucket name to be a domain of your choosing ala files.yourdomain.com, add a CNAME pointing to s3, and they will automatically determine that the files should come from your public bucket, using a little bit of internal rewriting. </p>