When I insert Folder images weight 120 MB "Library" increase of 1.98 GB

Or a folder with 1500 jpg 1024x768 . la folder weighs 120 MB in total but when I inserting the folder with 1500 images in Unity3D 4.5 The "Library" folder that weighs 300MB , increases in 1,98 GB after inserting images that weigh a total of 120 MB How is it possible that a folder that weighs 120 MB total ,face increasing Unity3D The folder "Library" in 1,98 GB someone can explain me why? Thanks PS. The size of the Library folder project after you build it Total Project 1.65 GB before inserting the final project images exported was 150 MB