iSlimPhoto is an application developed by Idealistic Future Ltd. iSlimPhoto can compress your photo library in such way that it will save alot of space without losing quality.
This is possible by using the setting "perfect" when compressing; this way photos will be reduced to the resolution of your display, and the rest of the extra-pixels will be wiped out.
The application is very useful when you need some more disk space, or when you want to move your library onto a new computer with less storage space.