Frank,
You need to name the file then add a ".jpg" to them, otherwise even your server does not regnize them and a proper format, and few (if any) people will just download and rename a file for fear of it being virus infected.
Bill S.
PS: For example:
http://www.bills2.us/tim/DSCN4493.JPG
When opened from my server looks like this:
While your files cannot be opened directly from your server due to the lack of the proper file extention(s)
Notice the file extention of ".JPG"