Text 270, 122 rader
Skriven 2005-02-28 21:42:00 av John <jtk93063-Nrvbmisc01 (1:278/230)
Ärende: Re: Beginner JPG header question
========================================


"Elef" <m.p.b@*toglimi*rocketmail.com> wrote in
news:hHFUd.72278$2h5.37963@tornado.fastwebnet.it:

>
> "Jason Keats" <jkeats@melbpcDeleteThis.org.au> ha scritto
> nel messaggio news:cvv001$f8v$1@possum.melbpc.org.au...
>> John wrote:
>>> John <jtk93063-nrvbmisc01@KILLSPAM.com> wrote in
>>> news:Xns960A8ADFC5F3DValhalla@64.164.98.6:
>>>
>>>> Hello Group,
>>>>
>>>> I posted in the other VB group and it was quite a long
>>>> post so I don't think anyone will answer it LOL.
>>>>
>>>> However, it seems I'm finding a bit of information on my
>>>> own. The really BIG hurdle I have is this.
>>>>
>>>> I am going to a site (or several sites) that post a .jpg
>>>> file. Sometimes the update it quite regularly, sometimes
>>>> it stays out there for a day or so.
>>>>
>>>> What I would like to do, exclusive of checking the
>>>> regular file name (say, XYZ.JPG), is to be able to
>>>> examine the JPG header to see if it is the same picture
>>>> as downloaded before, or if it is different.
>>>>
>>>> I am assuming that internally, the jpg file might store
>>>> it's original file name, or some other identification
>>>> exclusive that that individual picture.
>>>>
>>>> I've been Googling until my head hurts, and can't seem
>>>> to find the information I need. It seems there was
>>>> something out there in the 1992 to 1998 time frame, but
>>>> now it is not available. (I'm not sure if it was an ocx,
>>>> dll or what.)
>>>>
>>>> Anyway, does ANYONE know of a snippet or source
>>>> available on the web, or here for posting, where a
>>>> beginner can get information such as described above?
>>>>
>>>> Or perhaps someone may have another suggestion? (I
>>>> already have a procedure I'm working on where I compare
>>>> the filename and size. But this seems more academic,
>>>> because after I save the file on my HD it's got the
>>>> current time stamp and not the original one ... and the
>>>> user always posts the jpg file name with the same
>>>> prefix, i.e. XYZ for XYZ.JPG. So I'm more or less just
>>>> chasing in circles on this).
>>>>
>>>> TIA for any ideas, snippets, links to code, etc.
>>>>
>>>>
>>>>
>>>
>>> Oh, now this is what happens when I post something while
>>> on pain meds for my back LOL!
>>>
>>> I forgot to mention, he more often than not has a TEXT
>>> box in the JPG which states the time, date, and some
>>> other information, when he compiled the chart. Perhaps
>>> there is a way to search for the text box and read the
>>> text itself, as a string, and compare it to the previous
>>> JPG that was posted?
>>>
>>> OK, that's it ... sorry for the add-on post.
>>
>> Information on the JPEG file format is available at:
>>
>> http://www.wotsit.org/search.asp?page=5&s=graphics
>>
>> Text within a picture is not accessible without using OCR.
>>  Good luck with that!
>>
>> I'm assuming you already know how to download webpages,
>> etc.
>>
>>
>
> Fully agree with Jason. You may assume as the original name
> of the jpg is its MD5 hash. This way you'll be able to
> identify two identical images even if they are named
> differentely. You can find plenty MD5 hashing routines for
> VB on the web. Hope it helps
> Marco
>
>

Thanks Marco!

Whew. I've never worked with Crypto or digital signatures.

I've found a few resources on the Web and it seems fairly
straight forward though. So I'm just looking for a source code
example.

Seems what I have to do is:
    	When I save the first file, give it a unique file name
    	    	(I'm thinking of giving it a date/time name)
    	Get the digital signature of the first file
    	Download the new file and save with date/time filename
    	Calculate the digital signature of the new file
    	Compare the two
    	    	If equal, delete the new file else keep it

Simple. Just have to figure out the MD5 hash LOL.

Thanks again to both of you, Jason and Marco. This looks like
it's gonna be fun :)

--

John Kalenda
Simi Valley, CA
------------------
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