CDN file privacy for photos

[Heidieker]

CDN is almost completely new to me, so I have a basic question about security and privacy.
If I upload files like photos to a CDN, are they potentially visible or accessible to anyone, or are they normally protected by default settings (e.g. private URLs, access control)?
I would like to understand how public or private files on a typical CDN really are.
Or is it also possible to store images on my own server and not use the CDN (or only use it optionally)?

[Smaug6739]

Uploaded files on the CDN are not protected with auth but the url is private (randomly generated). You can also use another (potentially secured) server