This is an automatic Thumbnail creator.
Each picture in your Shop will be chached in the "/catalog/images/imagecache" directory in the right
size and with the same name as the original.
The size is set in the Admin panel under Configuration - Images.
These values are the max values. The thumbnail will be created in the right proportions.
The tumbnail will be created an th first time the picture is call in the Shop.
Once an thumbnail is created it will always be used until you change the size in the Admin panel.
If you delete an image, you have also to delete the thumbnail in the "/catalog/images/imagecache" directory manually
Installing should be quite easy, only one file tho change.