如何授予对特定云服务的s3图像URL访问权限

When an image is uploaded in s3 by default the urls are private. I can make them public by adding permissions on the console but i don't want to do that for every image, want to automate it. I am using a non AWS cloud services for which accesses the image via the url. The service cannot access the image because the urls are private. How do i make the urls public to particular service? Making the entire bucket public is not an option. When an image is uploaded in s3 by default the