How to save uploaded images to another server

Many large websites use second-level domain names to call images. If the files bound to the second-level domain name and the primary domain name are not on the same server, what if I save the image uploaded from the primary domain name address to the second-level domain name binding file and return an absolute address? Many large websites use second-level domain names to call images.
If the files bound to the second-level domain name and the primary domain name are not on the same server, what if I save the image uploaded from the primary domain name address to the second-level domain name binding file and return an absolute address?

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Many large websites use second-level domain names to call images.
If the files bound to the second-level domain name and the primary domain name are not on the same server, what if I save the image uploaded from the primary domain name address to the second-level domain name binding file and return an absolute address?

Does segmentfault do this? When you upload an image and call the upyun api image to upload it to upyun, a url is returned and finally presented to the user. This is the CDN url ~
Http://sfault-avatar.b0.upaiyun.com/405/397/4053973633-561483bccecdd_big64

How can I save it to another server.
First, you can have the same or different domains for different servers.
(Enter it later)

You can directly send the image encoding to the corresponding server interface and save the image as a file on the server.