create a bucket policy with the following JSON:
{
"Version": "2008-10-17",
"Statement": [{
"Sid": "AllowPublicRead",
"Effect": "Allow",
"Principal": { "AWS": "*" },
"Action": ["s3:GetObject"],
"Resource": ["arn:aws:s3:::bucket/*" ]
}]
}
Important: You should replace bucket in the Resource line with the name of your bucket.