Why do I get Access denied on s3 asset source images?
I'm not really an AWS expert, but I think if you want to allow public access to an S3 bucket, then it should look something like this:

{
    "Sid": "PublicReadGetObject",
    "Effect": "Allow",
    "Principal": "*",
    "Action": "s3:GetObject",
    "Resource": "arn:aws:s3:::bucketname/*"
}