Everyone gets confused when it comes to song covers. You've listened to the original so often before, have hummed it, have seen the video, have basically identified that song to belong to the artist who sang it in the first place. Some songs though, have been covered by different artistes so many times, that one could hardly remember the original version anymore. Songs like "Heaven" by Bryan Adams, or "I will survive" by Aretha Franklin, or "We will rock you" by whoever it was that orignally sang it. 

Most songs that are covered sounds almost exactly like the original, which really...isn't very original. If you have to cover a song, make it sound so different, that it becomes your version that people would like better. Enter David Cook singing Mariah Carey's 'Always be my baby'. 

 That was my favourite song by Mariah Carey. Ever. But now I almost prefer the David Cook version. :P