.ITC File Extension
What is an ITC file?
Contains album artwork and metadata for songs that have cover artwork; used by iTunes to speed up browsing songs in Cover Flow mode; saved by default within the ~/Music/iTunes/Album Artwork/Local/... directory.
ITC files are referenced by iTunes but are not meant to be opened manually. You can download album artwork for songs in your iTunes library by selecting "Get Album Artwork" from the Advanced menu in iTunes.