I recently noticed that the Album Artwork folder in my iTunes folder (~/Music/iTunes/) has more than doubled in size. I recall, not long ago, that it was around 2 GB, but it is now around 4.6 GB, for roughly the same amount of music. (About 80,000 tracks, or just over 5,000 albums; the album number is more important, as there is only one cache file stored per album.)
The Album Artwork folder is a cache folder that iTunes uses to quickly display album art in the program’s different views. It contains three sub-folders:
- Cache, which is the cache for album art embedded in files in your iTunes library
- Cloud, which is a local cache for album art embedded in files in the cloud, if you use iTunes Match
- Download, which stores album art that you downloaded from the iTunes Store, either when you purchased content, or when you used iTunes to find artwork for music you ripped (right-click on one or more tracks, then choose Get Album Artwork).
As you scroll through your iTunes library, the program reads the album art in files or linked to them, and displays artwork in the program’s window. All the cache files do is allow iTunes to display art more quickly, rather than having to extract the artwork from the ID3 tags in music files when it wants to display it.
So, at some point, iTunes must have changed the way artwork is saved in this folder. I notice that the majority of my artwork files in the cache folder – these are .itc files – are 969 K. Some of the files are slightly smaller, and some are much smaller, but most end up being the same size. But I’m very careful to keep most of my album art around 100 K or smaller; when I find art on the Internet, I scale it to 600×600 (if it’s larger than that), then save as JPG, and make sure to compress enough to keep the files small.
I have always had this folder excluded from my Time Machine backups, so I can’t see when the size changed. If any of my readers can check in their Time Machine backups, I’d be interested to find out if their folders have increased in size, and, if so, when. My guess is that something was changed in iTunes 10.5 or 10.5.1 which altered the format of cache files, or changed their size.