I attach a patch against 3.3; this is substantially Dave Chambers' original patch with a trivial test added and a doc change. This means that HKCR is scanned to determine extensions and these will override anything in the mimetypes db. The doc change highlights the possibility of overriding this by passing files=[].

I can't see an easy solution for this which will suit everyone but I've sat on it waay too long already. The module startup time is increased but, for bugfix releases, I can't see any other solution which won't break compatibility somewhere. 

I'm taking the simplest view which says that: .jpg => image/pjpeg is broken but that the winreg code has been in place for too long to simply back it out altogether.

I'll commit appropriate versions of this within the next day to 2.7, 3.3 and 3.4 unless anyone objects. Please understand: this *is* a compromise; but I don't think there's a perfect solution for this, short of the rethink which mimetypes needs per MALs suggestion or otherwise.