All About Images [link – the table of contents] is a University of Michigan research guide:
Images are very important for the visual presentation of your document, presentation or website. However, working with images can sometimes be difficult because we have to consider things like resolution, image size, file size, and color mode.
This guide is meant to help clarify and answer some common image questions, such as why photos print blurry, what file type should I use, and what’s the difference between changing resolution and resizing.
Use GIMP To Resize An Image Just follow the step-by-step instructions.