>>Any site subject to bot attacks may use this technique. I've seen a number of them e.g. the NSI WHOIS lookup page: https://www.networksolutions.com/whois/index.jsp . Enter a domain name, and you have to complete the picture CAPTCHA to proceed.
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>Yes, but WHOIS is about requesting information. There is no login. That would then be a normal procedure, such as many sites using the same for receiving testimonials, assuring, as you said, not receiving requests from bots. But, in my case, I was referring to a site, where we actually have an account, and log in on a regular basis. It's like here. Imaging you would have to do that after each login.

Unless you have a contract that says you don't have to use a CAPTCHA when you log on, the site operator can do whatever they want. Users who don't like it can vote with their feet.

Every site and organization strikes a balance between convenience and security. The site you describe leans more towards security.