IE7 changes image MIME type

Trying to upload a PNG or JPG image to a website fails. IE7 has changed the
MIME types from image/jpeg to image/pjpeg and image/png to image/x-png,
neither of which is accepted by the site.
(a) Why does IE do this?
(b) Can I stop it from doing this?

I read at

http://msdn.microsoft.com/en-us/libr...47(VS.85).aspx

When uploading files from the client to the Web server, Windows Internet
Explorer uses FindMimeFromData to determine a MIME type. Where possible,
FindMimeFromData returns hard-coded values from the list of Known MIME Types
rather than relying on the MIME type value associated with the file extension
in the system registry. In some cases, the detected MIME type can differ from
the generally accepted value for backwards compatibility, as shown in the
following table:

Standard MIME Type FindMimeFromData Returns
image/jpeg image/pjpeg
image/png image/x-png


but I'm none the wiser.

--
Noel

[Also posted at answers.live.com - just to compare the performance of the
two sites]

"Ildhund" <> wrote in message news:9B488B52-E1FE-43EB-AE4C-...
> Trying to upload a PNG or JPG image to a website fails. IE7 has changed the
> MIME types from image/jpeg to image/pjpeg and image/png to image/x-png,
> neither of which is accepted by the site.

> (a) Why does IE do this?


Supposedly it is part of MIME sniffing.


> (b) Can I stop it from doing this?


Disable it using the Security settings option

( Disable ) Open files based on content, not file extension

(Tip: it's in Miscellaneous section, so press M and O to find it.)


HTH

Robert
---


>
> I read at
>
> http://msdn.microsoft.com/en-us/libr...47(VS.85).aspx
>
> When uploading files from the client to the Web server, Windows Internet
> Explorer uses FindMimeFromData to determine a MIME type. Where possible,
> FindMimeFromData returns hard-coded values from the list of Known MIME Types
> rather than relying on the MIME type value associated with the file extension
> in the system registry. In some cases, the detected MIME type can differ from
> the generally accepted value for backwards compatibility, as shown in the
> following table:
>
> Standard MIME Type FindMimeFromData Returns
> image/jpeg image/pjpeg
> image/png image/x-png
>
>
> but I'm none the wiser.
>
> --
> Noel
>
> [Also posted at answers.live.com - just to compare the performance of the
> two sites]

"Robert Aldwinckle" wrote:
> "Ildhund" <> wrote...
> > Trying to upload a PNG or JPG image to a website fails. IE7 has changed the MIME types from image/jpeg to image/pjpeg and image/png to image/x-png, neither of which is accepted by the site.
>
> > (a) Why does IE do this?
>
> Supposedly it is part of MIME sniffing.
>
> > (b) Can I stop it from doing this?
>
> Disable it using the Security settings option
>
> ( Disable ) Open files based on content, not file extension
>
> (Tip: it's in Miscellaneous section, so press M and O to find it.)

Thank you, Robert, but no joy, I'm afraid. I had that setting to start with;
I changed it, re-started IE7, changed it back and re-started again. Then I
tried an upload, and this is what Fiddler says I'm posting:

Content-Disposition: form-data; name="Filedata";
filename="G:\Documents\Noel\My Pictures\Screenshot.PNG"
Content-Type: image/x-png

and the site responds with

[The content type of this image is not allowed.]

so that setting seems not to affect outgoing traffic.
--
Noel

"Ildhund" <> wrote in message news:F1840B43-7FA0-4BB0-A7E0-...
> "Robert Aldwinckle" wrote:
>> "Ildhund" <> wrote...
>> > Trying to upload a PNG or JPG image to a website fails.
>>> IE7 has changed the MIME types from image/jpeg to image/pjpeg
>>> and image/png to image/x-png, neither of which is accepted by the site.
>>
>> > (a) Why does IE do this?
>>
>> Supposedly it is part of MIME sniffing.
>>
>> > (b) Can I stop it from doing this?
>>
>> Disable it using the Security settings option
>>
>> ( Disable ) Open files based on content, not file extension
>>
>> (Tip: it's in Miscellaneous section, so press M and O to find it.)
>
> Thank you, Robert, but no joy, I'm afraid. I had that setting to start with;
> I changed it, re-started IE7, changed it back and re-started again. Then I
> tried an upload, and this is what Fiddler says I'm posting:
>
> Content-Disposition: form-data; name="Filedata";
> filename="G:\Documents\Noel\My Pictures\Screenshot.PNG"
> Content-Type: image/x-png
>
> and the site responds with
>
> [The content type of this image is not allowed.]
>

> so that setting seems not to affect outgoing traffic.
> --
> Noel


Sorry, Noel. I had completely overlooked that this is an upload scenario.
You're right; I wouldn't expect that option to affect that case.

Now my only suggestion would be to try using ProcMon, for Registry
accesses, hoping that that could give you a clue to a possible
HKCU override you could devise and use.


Good luck

Robert
---

"Robert Aldwinckle" wrote:
> "Ildhund" wrote...
> > "Robert Aldwinckle" wrote:
> >> "Ildhund" <> wrote...
> >> > Trying to upload a PNG or JPG image to a website fails.
> >>> IE7 has changed the MIME types from image/jpeg to image/pjpeg
> >>> and image/png to image/x-png, neither of which is accepted by the site.
> >>
> >> > (a) Why does IE do this?
> >>
> >> Supposedly it is part of MIME sniffing.
> >>
> >> > (b) Can I stop it from doing this?
> >>
> >> Disable it using the Security settings option
> >>
> >> ( Disable ) Open files based on content, not file extension
> >>
> >> (Tip: it's in Miscellaneous section, so press M and O to find it.)
> >
> > Thank you, Robert, but no joy, I'm afraid. I had that setting to start with;
> > I changed it, re-started IE7, changed it back and re-started again. Then I
> > tried an upload, and this is what Fiddler says I'm posting:
> >
> > Content-Disposition: form-data; name="Filedata";
> > filename="G:\Documents\Noel\My Pictures\Screenshot.PNG"
> > Content-Type: image/x-png
> >
> > and the site responds with
> >
> > [The content type of this image is not allowed.]
> >
>
> > so that setting seems not to affect outgoing traffic.

> Sorry, Noel. I had completely overlooked that this is an upload scenario.
> You're right; I wouldn't expect that option to affect that case.
>
> Now my only suggestion would be to try using ProcMon, for Registry accesses, hoping that that could give you a clue to a possible HKCU override you could devise and use.

It looks as if the conversion is hard-wired into urlmon.dll. In the
meantime, the question has become a trifle academic: those responsible for
the forum concerned have tweaked their upload procedure to allow both
image/pjpeg and image/x-png. It's still extremely annoying, though, and there
must be many sites where this arbitrary interference by IE causes problems.

Thanks as always for your interest.
--
Noel