ImageCache is a fantastic, flexible module that provides a permitted user the ability to create a variety of different image presets that can be applied to images uploaded via an image field in a custom content type.
Many different actions are available, including auto-scaling and cropping, watermark application, and corner rounding. The original, uploaded image is not affected, instead, a copy of the uploaded image is made, processed, and then automatically stored in the imageCache directory under an auto-generated directory name.
These presets can be applied to node and teaser displays in the CCK Display configuration tab and via Views field settings.
The beauty of this is that you can upload a single image, and then change the display on the fly as needed, and the changes will cascade down through all content or Views results that contain that particular imagefield.
Read on to discover some of the interesting things you can do with Imagecache.