what application has the .jpg file extension.  Is there a list of file
extensions and related appliction

Hi! Thanks for the question.

The .jpg extension is a jpeg image file and can be viewed by any image
viewer software like Paint or even in your own browser.

"File Extension Details for .JPG"
http://filext.com/detaillist.php?extdetail=JPG


The Filext website also has a list of file extensions and related
applications. If it doesn't list the application, like for the .jpg
file, then it is generally supported by numerous programs.

Filext
http://filext.com/

Search terms used: 
application extension list

I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
                 
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Easterangel-ga                 
Google Answers Researcher

Filext.com has a ton of file extensions, but uses a rather confusing
interface.  I think FileInfo.net (http://www.fileinfo.net/) is much
easier to use.

You can also browse a list of all image file types at the website,
including .JPG files at:
http://www.fileinfo.net/filetypes.php?image

Hope this helps!