If it adds to the content, then it is worth something. So make someone worth something.
If it doesn't matter, add a random screenshot of kernel code.
The "worth something" doesn't even have to be financial.
Find a nice image that someone has made which is linux-related, and ask if you can use it & credit the author.
If no, try someone else.
If that's too much work, use a random screenshot of kernel code ...
There are artists out there that have already freely shared some really cool art, that would love to be able to point to publications that they have permitted to use it.
If you have some budget, pay them. Value the time involved.
Just not AI filler BS. I'm not going to see some filler AI art and go "oh yeh, I'm going to use that for X/Y/Z".
But if I see some cool art, I'm inclined to commission something for an actual use case
From something like LetsEncrypt?
As an HTTP-01 Challenge? Not an DNS-01 challenge?
Http challenge means that port 80 is accessible from the public internet (because that's how LE can confirm it can reach your server via the public DNS records, proof of server ownership).
DNS-01 is about proof of DNS record ownership, and doesn't prove public internet access.
Also, what are you self hosting?
Does it really need to be publicly accessible? Or just accessible by you and people you trust?