A computer has to be told which program to use to open what. Most emailed pictured are in a format called JPEG or JPG, some are in another format called GIF, and some, fewer still, are in a format called TIFF. If you haven't mapped an application to these file types your computer will balk at opening them. There are also a few more obscure and less often used image types which can make the computer choke. Some require proprietary programs to open. For example, Phtoshop saves files in a formats it likes to be the only one to open.

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