Direct download.
bamter.org is hosted at MomentoVPS - https://momentovps.com/
They take payment via BTC, which is why we use them. However, they are very unreliable, even for a cheap virtual hosting place. This means the bamter.org site is sometimes offline.
If anybody knows of a better VPS/hosting solution that takes BTC, lemme know.
Downloading images from unofficial sources is not recommended. As you found with the corrupt download and 404s, they often just don't work. You also run the risk of tampering or malware infected images if you choose not to use official mirror sites.