A JPEG image should be used when faster upload times and less storage space usage is necessary. JPEG's reduce the size of an image by up to 15 percent without losing quality, making it the ideal format for web pages.
Other common file types for saving images include GIF and PNG. These file formats are best used for images that are displayed on the web. The GIF format is most often used for short animations. It is rarely used for photographs, as it reduces the image to 256 unique colors. PNG images are best used for logos or other images that require transparency.