Thinking that there’s no way built into Mac OS X to resize images, I have been for a long time hunting down free third-party image resize applications. What I did not know and could not find until today is that the Preview application, which is used to preview images by default on Mac OS X, has a convenient resize feature built right into it. It is found under the Tools menu, aptly named “Adjust Size“.
One apparent gotcha that can bite you crazy about resizing using Preview is that after adjusting the size for an image, the preview of the image will shrink considerably to a size smaller than you would expect. Don’t let that mislead you. Once you save the image, Preview will re-display the image in the proper, expected size.