Why do i have 2 of the same pictures on my computer

Question

When i import photos there always ends up being 2 of them... i always select don't add duplicates. But for instance when I put a picture in it goes under to categorires
My name->Pictures->Iphoto Library->Masters->2008->Roll 92->Image name               then that same picture is under this aswell
My name->Pictures->Iphoto Library->Thumbnails->2008->Roll 92->Image name
It takes up double my space so it turns 4000 pics into 8000. Can I delete one of them without losing the original and is there an easy way to do this? also how do i prevent this from happening when i import more photos Thanks
My computer is Mac book Pro and i have the most recent Iphoto

Answer 1

1 - that is how iPhoto works and no you can not change it
2 - you can not ever delete anuything from the iPhoto library unless you do it using iPhoto - in fact you should not be going into the iPhoto library at all - there is no reason to be there
3 - it is not taking double the space - thumbnails are very small
4 - and when you make any modifications to any photo a third version is created - the modified version - and again that is the way iPhoto works
5 - the only way to prevent this is to use a different probram that does no work this way (there are a number of very good reasons why iPhoto and other DAMs - Digital Assett Managers - work this way including keeping the digital negative, non-destructive editins, etc
LN