If for some reason you want to download a CD image, try searching the mailing list archives for possible sources. Of course, any OpenBSD ISO images available on the Internet either violate Theo de Raadt's copyright or are not official images. The source of an unofficial image may or may not be trustworthy, it is up to you to determine this for yourself. We suggest that people who want to download OpenBSD for free use the FTP install option. There are numerous international mirror sites offering FTP access to OpenBSD releases and snapshots.
AFS access is also available.
You should always use the site closest to you. Of course, your OpenBSD release CD is always closer than any mirror. Generally the best way to get started with a current source tree is to install the source from the most recent CD and then configure AnonCVS to update it regularly. If that's your situation, then starting with a recent release CD is even more important. Yet another alternative is to get the source code from the web.