Why does IE7 specify a mime-type of image/pjpeg rather than just image/jpeg?

Question

When uploading a file (jpeg) via a form in IE7 I am seeing a mime-type of \"image/pjpeg\" instead of \"image/jpeg\" (as I see in Firefox or similar). It\'s easy enough to work

Answer 1

IE can upload all .jpeg files as its hack MIME type 'image/pjpeg' regardless of whether or not they're actually progressive.

Don't rely on the MIME type supplied in a file upload, there is every chance it could be wrong for a variety of reasons including this one.