On Sun, 01 Mar 2009 20:33:57 +0000, eax@less.than wrote,
>On 01 Mar 2009 19:22:42 GMT, "mr.bill" <mr.bill@invalid.lss> wrote:
>
>>The final two were progressive which meant the stripped out headers were
>>unique to each image.
>
>Do you know the format of APP14 segment for progressive jpegs? I spent
>a lot of time searching in google but found nothing. Only first 12
>bytes of APP14 are well documented. But APP14 segment of progressive
>jpegs contains extra bytes, which are different for each image. Now my
>checking program simply ignores those extra bytes and let them be
>different.
>
My experiments with those progressive images for which I had the originals
led me to the conclusion the unique bytes were based on what happened when
compressing the jpeg from the camera image. Further recompression at the
same settings as the original compression duplicated some of the bytes,
came close to duplicating a couple, meaning they could be guessed, but left
at least 8 bytes unknown. Guessing at all combinations of 8 bytes by
hand until a match was found would happen at about the same time as the
heat death of the universe. No thanks!
--
mr.bill
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