php upload an image after modifying its extension [closed]

Question

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.

Closed 9 years ago.

I'm working my way through input filtering (files) and I just discovered that if you rename a .jpg file into a .png file the MIME type will change automatically to fit the extension. So I was thinking, in that case what's the point of checking the MIME type ? (I know that it can be changed by the client which is a serious drawback too, but I'm checking it "for fun")

Answer 1

Well, for one, the content of the file doesn't change; so if you actually check the type yourself (instead of blindly trusting user-submitted data), you'll see it's just a misnamed file.

As for the user-supplied MIME-type, checking that is an exercise in futility, yes.