If you are using Amazon S3 for hosting images, you can consider using their their new CloudFront service for content delivery. Like Amazon S3, CloudFront is inexpensive (you pay for what you use) and gives all the benefits of a typical CDN service.

When you upload files to Amazon S3 and configure them with CloudFront, a copy of S3 files will be cached in various Amazon servers that are spread across important cities in US, Europe and Asia. So a visitor from India will be served content by the server located in Asia and so on – see illustration above for location of all Amazon servers.

Source: http://www.labnol.org/internet/setup-content-delivery-network-with-amazon-s3-cloudfront/5446/