Or at least, the following line doesn't work anymore: https://github.com/metabrainz/libcoverart/blob/b328625410b7a8830ed4fe25e43ba9bad078553f/examples/example.cc#L89.:
I've tracked this down to the following problem: after a few redirects, the index.json will be retrieved from http://ia902607.us.archive.org/cors_get.php?path=%2F32%2Fitems%2Fmbid-76df3287-6cda-33eb-8e9a-044b5e15ffdd%2Findex.json (different host names etc. are possible, of course). However, in https://github.com/metabrainz/libcoverart/blob/b328625410b7a8830ed4fe25e43ba9bad078553f/src/HTTPFetch.cc#L210 URI.Path() is only:
The IA responds to that request with HTTP 417.
This might be related to https://github.com/metabrainz/coverart_redirect/commit/1f54546533e0336f21bdc170c9d0379b89d0664f.