When I make a HEAD request for an image in the Cover Art Archive I get
a content length of 1 for the image.

My understanding is that either the Content-Length should be equal to
the length of the content if I had made a GET request, or the header
should be absent (ref
http://stackoverflow.com/questions/3854842/content-length-header-with-head-requests
).

Sample HEAD request:

Request
HEAD http://ia601207.s3dns.us.archive.org/mbid-fb70321f-78df-30ff-92de-21a4bc9ca16c/mbid-fb70321f-78df-30ff-92de-21a4bc9ca16c-900033833.jpg
Headers:
[Accept-Encoding: gzip
, User-Agent: bliss/Development mode +http://www.blisshq.com
, Host: ia601207.s3dns.us.archive.org
]

Response

Headers:
[Server: nginx/0.8.54
, Date: Wed, 23 May 2012 09:26:26 GMT
, Content-Type: image/jpeg
, Connection: keep-alive
, Accept-Ranges: bytes
, Content-Length: 1
, x-upload-date: 2012-05-09T02:13:11.000Z
, x-archive-meta-collection: coverartarchive
, last-modified: Wed, 09 May 2012 02:13:02 GMT
, ETag: "4ee00e1e2fbace73636d4f2633f7d2ef"
, x-archive-auto-make-bucket: 1
, x-archive-meta-mediatype: images
, Expires: Wed, 23 May 2012 15:26:26 GMT
, Cache-Control: max-age=21600
]

Equivalent GET request:

Request
GET http://ia601207.s3dns.us.archive.org/mbid-fb70321f-78df-30ff-92de-21a4bc9ca16c/mbid-fb70321f-78df-30ff-92de-21a4bc9ca16c-900033833.jpg
Headers:
[Accept-Encoding: gzip
, User-Agent: bliss/Development mode +http://www.blisshq.com
, Host: ia601207.s3dns.us.archive.org
]

Response

Headers:
[Server: nginx/0.8.54
, Date: Wed, 23 May 2012 09:28:26 GMT
, Content-Type: image/jpeg
, Connection: keep-alive
, Accept-Ranges: bytes
, access-control-allow-headers:
authorization,x-amz-acl,x-amz-auto-make-bucket,cache-control,x-requested-with,x-file-name,x-file-size,x-archive-ignore-preexisting-bucket,x-archive-meta-title,x-archive-meta-description,x-archive-meta-language,x-archive-meta-mediatype,x-archive-meta01-subject,x-archive-meta02-subject,x-archive-meta03-subject,x-archive-meta04-subject,x-archive-meta05-subject,x-archive-meta01-collection,x-archive-meta02-collection
, x-upload-date: 2012-05-09T02:13:11.000Z
, x-archive-meta-collection: coverartarchive
, last-modified: Wed, 09 May 2012 02:13:02 GMT
, ETag: "4ee00e1e2fbace73636d4f2633f7d2ef"
, x-archive-auto-make-bucket: 1
, access-control-allow-origin: *
, access-control-allow-methods: GET,POST,PUT,DELETE
, x-archive-meta-mediatype: images
, Content-Length: 383681
, Expires: Wed, 23 May 2012 15:28:26 GMT
, Cache-Control: max-age=21600
]

Note the difference in Content-Length.