As anon above said, they can be watermarked.
Easiest way to check is compare hash (md5,sha,...) of your copy and someone else's copy.
If they are same, you can upload it (but be safe, use vpn, post from public wifi or something, recently YTS ratted out its users )
If they are not same, google 'binary diff'. Then you can remove/edit the parts that differ and which presumably identify the owner.
