Article: David Archuleta's performance of John Lennon's "Imagine" was considered by many as one of the best of the season. Jennifer Lopez, who was brought in as a judge in season ten, called it a beautiful song-moment that she will never forget. Jason Castro's semi-final performance of "Hallelujah" also received considerable attention, and it propelled Jeff Buckley's version of the song to the top of the Billboard digital song chart. This was the first season in which contestants' recordings were released onto iTunes after their performances, and although sales information was not released so as not to prejudice the contest, leaked information indicated that contestants' songs frequently reached the top of iTunes sales charts.

Now answer this question: On what digital platform were contestants performances released to after airing on American Idol?
iTunes