Good morning,
I am using amazon s3 bucket as the image server. And I want to use a subdomain of my site, how to address this bucket. eg: a picture is now in: https:/
You need to rename your bucket to match the custom domain name (e.g. imagens.mydomain.com.br) and set up that domain as a CNAME to
(in your case imagens.mydomain.com.br.s3.amazonaws.com.
The full instructions are available here:
http://docs.aws.amazon.com/AmazonS3/latest/dev/VirtualHosting.html