.jpg (versus .jpeg/.JPG) files not being displayed

[speakman]

Image files with the extension .jpg are not being displayed
on my sonic-hosted web page, but if I change them and their
html references to .jpeg or .JPG, they are displayed.

I have a local .htaccess file with:

AddType image/jpeg .jpg

in it, but this does not seem to solve the problem.
Can anyone shed some light on the reason for this, and
suggest some other solution?

Thank,
Tony S