Loss of hard disk space

Hi,

I recently bought myself a new computer with a dvd burner and have been burning copies of my wedding for friends and family. I’ve been using Nero to do so and have found that I’m losing disk space each time I make a copy of it. I’ve now lost 10 gigs of disk space with only doing 5 copies. Can anyone tell me why? I did a disk cleanup to no avail and am currently doing a disk defrag which hasn’t done anything. Why is this happening and how can I get it back?