How to determine whether a picture is accelerated by cdn?

I have an interview this week. If you can"t answer this question, you should ask the interviewer below, but I forgot.
I remember my answer is to see whether the domain name is a well-known cdn cloud service provider, but some cloud service providers will also provide your domain name binding service. So. A distressing question for me

to put it simply, it is a picture.. How do we tell if he is accelerated by cdn

May.22,2021
The quickest way to

is to see the response header. If it includes x-cache , via , x-via and other fields, cdn acceleration is basically used.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b41e6c-2b932.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b41e6c-2b932.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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