How to Determine the DPI of a JPEG
The JPEG file format is popular because it can balance image quality against file size. For example, if you're not concerned about the file size, you can keep the image quality very high. On the other hand, if files need to be compact for easy emailing or storage, you can reduce the image quality to a lower -- but still acceptable -- level. The DPI (dots per inch) determines the resolution of the image: the higher it is, the better it will look for printing. Windows comes with a program called Paint, which you can use to determine the DPI of your JPEG images.
Click the Start button and choose "All Programs." Then select "Accessories" and "Paint" to display the Paint window.
Click the "File" button and choose "Open" to display the Open dialog box.
Navigate to the JPEG whose DPI you'd like to determine. Double-click the icon to open it in Paint.
Click the "File" button and choose "Properties" to display the Image Properties dialog box. The DPI of the JPEG will be listed next to Resolution.