Currently tlwebadm relies on the legacy Microsoft ICO favicon system. We should use a proper image format (like PNG) and also stop using the deprecated method of putting it as /favicon.ico.
It seems most web pages still use ICO files for favicons in 2022. This method is now used by both Web Access and Web Admin as of bug 7998.
We now reference the ICO in the HTML instead of placing it as /favicon.ico. See commit r39174.