Windows 7: Disable File Extension Recognition

I need to be able to upload jpeg files to our website and the software package I use for that requires that the filename be entered in lower case in the format "filename.jpg"

However, I've recently upgraded from XP to Windows 7 and note that JPG is being added in uppercase after my typed fileneme so that I end up with "filename.jpg.JPG" which is rejected by the uploading software. My web designer tells me that this is attributable to automatic file type recognition in Windows 7, and not to the upload software.

How can I switch that off?

No such thing exists in Windows 7. Windows 7 is not going to change your file extensions on its own. I can tell you. The upload software is STUPID and poorly made. I bet it might also have a security hole. It should never rely on the file extension, even then it should not be case-sensitive. Who ever wrote this "Upload software" sorry to say is a retard.

* I've written countless file uploading packages for years in PHP and other web development languages. One never relies on client-side information about a file. NEVER. That means the filename is not to be trusted along with any other data.

Welcome to Seven Forums. Along with what logicearth pointed out, don't type the file extension (.jpg) when uploading.
It's odd you'd need to type in a file name to upload, it should already have a name, Windows won't allow no-name files.
This does sound like buggy 3rd party software, not a Windows issue.