Q: What is the format of the flags?
A: If not stated otherwise, it is the human-readable string the answer appears in naturally, e. g. if the challenge was to "Find my first name.", the flag would be "Michael". No curly brackets or anything. Usually case-insensitive if not stated otherwise.
However, if a flag format is given, the flag has to be given in that format, e. g. if the challenge was "When was this FAQ created? Format: DD.MM.YYYY", the flag would be "02.03.2023" instead of "03/02/2023".
If I add units, commas, brackets or any other readable characters to the flag format, those characters have to submitted, too, e. g. if the challenge was "How tall is the Eiffel Tower (Tip) in meters? Format: ### m", the flag would be "330 m" instead of just "330". If the flag format is given as "CTF{...}" the flag is something like "CTF{1234}" instead of just "1234". If the format is "xxx, (xxx)", the flag is something like "abc, (def)" instead of just "abc def".
Update: I made the flags more robust, so most of the above is not true anymore and most of the time, spaces and commas are optional. I also added examples for most answers to make it even clearer.
Some of my thoughts on flag formats: https://blog.michweb.de/?p=711

Q: I think my answer is correct, but it's not accepted. What do I do?
If you have already tried different formats and are really sure your answer should be correct, you can send me an email at the address stated in my legal notice (https://michweb.de/legal-notice/). If I agree with you, I will add your answer as a valid flag and may award you with some extra points.

Q: Is it okay to publish a write-up of the challenges?
Yes, absolutely. I would like to read it. :)

Q: Why does your so-called OSINT CTF have so many forensics and cryptography challenges?
That's because according to my understanding, finding details in closed data requires a similar mindset as finding things in open sources. Figuring out how to make things work often needs curiosity and research, which are also essential for OSINT investigations. Plus, I just enjoy forensics and cryptography myself.