1. Open the picture in an image editor. The easiest way to print the image at the correct size is to open it in an image editor, such as Paint in Windows or Preview in OS X.
2. Open the Page Setup window. This will allow you to ensure that you print in the correct dimensions. You can open this from the File menu in Paint.
3. Check the "Adjust to 100 percent normal size "option. This will set the image to print as its actual size, instead of attempting to fill up the entire page.