Deception

[ErfolgreichCharismatisch]

You wrote "Is open source and self-hosted, which gives you additional guarantees for data security" yet you have to sign up for their servers and register? What?

[calloatti]

You mean this?

That is your own self hosted server fyi.

[ErfolgreichCharismatisch]

What do I need a login for on my own server?

[calloatti]

For the same reasons you have to create a user and login in any modern operating system?

[pospielov]

First, CompreFace works locally so you can use it without the internet. We do not gather any sensitive information, except for anonymous statistics, and you can opt out of it during login.

As for "why do you need login on a self-hosted server," this is just a very simple measure to protect your data.
There is a possibility someone else has access to your network. To get access to CompreFace, he will need to register an account. Only the first user has full access. All new users won't have access to any applications or services until the first user will grant it. Here you can read more about how it works:
https://github.com/exadel-inc/CompreFace/blob/master/docs/User-Roles-System.md