The .jpg format has two main features: The Good Feature: The file is goes through a compression algorithm which makes the size smaller, therefore taking up less storage space. The Bad Feature: The file is goes through a compression algorithm which makes the size smaller, BUT when you open it again you'll find that the compression algorithm has also deleted some information. That causes a loss of fine details. But even with the loss it's still a VERY useful graphic format. Create your images at a higher resolution (600 dpi), then resizing to a smaller size doesn't hurt much. NEVER start with a lower resolution (150 dpi) and try to resize to a larger size.
