JPEG format - JPEG format is used mainly for web-based and computer-viewed applications. These jpegs are 72 dpi in resolution and RGB in color space format. They can be used with programs such as Microsoft Powerpoint.
PNG format - These files are full color, RGB color space format, 300 dpi resloution and have a transparent background.
PDF format - These PDF files are used in applications requiring full color, CMYK color space format, such as offset printing(magazine/newspaper). These files are 300 dpi in resolution and should be used when fine detail is required.
NOTE: To save an image, right click on the format and select "Save Target As..."