Hopefully you already know how great Preview is. It comes built in with every Mac, it handles PDFs and images with ease, and does a great deal of basic image editing just fine, saving you the bother ...
When it comes to knowing how to resize an image with GIMP, a basic resize is an easy process, as you'd hope. Open up your image in GIMP, click on "Image" along the top menu, then select "Scale Image" ...