Re: "Some Pictures Have Been Blocked.......
From: Vanguard (use_ReplyTo_at_domain.invalid)
Date: 03/01/05
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Date: Tue, 1 Mar 2005 15:36:43 -0600
"Jimmy" <JimmyCliff@xemaps.com> wrote in message
news:sK-dncv1H6O3SrnfRVn-jg@comcast.com...
> ...to help prevent the sender from identifying your computer." is at
> the top of my emails from Comcast (and maybe other email?) and I am
> curious how this works. If I view pictures or choose not to view
> pictures that others send me in email I can control the senders
> ability to identify my computer? I just don't understand this one. How
> can I send someone an email and get to ID their computer if they open
> the photo I send? What kind of IDing? IS this whole thing just a
> Comcast dream or is this real.
>
> J.
>
If the picture is inline with the body of the e-mail (i.e., it is
embedded as a MIME part that encodes the picture) then the sender cannot
see when you view that picture anymore than they know you viewed some
text within the body of the message.
However, if the image is a link back to a file on someone's server then
that server knows when you viewed your e-mail. Why? Because your
e-mail client, when it rendered the HTML-formatted message, has to yank
the file for that image from some external file server. If the image is
unique to your e-mail then the server knows that the e-mail that
included that unique image file has been opened and rendered for
viewing. Those are called web bugs or beacons. They are only effective
in HTML-formatted e-mails where the e-mail client is configured to
render that HTML coded message to present the images and all other
formatting.
If you read your e-mails in plain-text mode then the linked images never
get yanked from the external file server. However, that also means you
won't see any of the inline pictures, either, and they will appear as
attachments that you have to open separately. Some e-mail clients, like
Outlook 2003 and Outlook Express 6, will let you block *linked* images
(but leave inline images alone). Alternatively, you can use anti-spam
products that will block linked images. I still use Outlook 2002 which
doesn't have the linked image block feature, so I use SpamPal with its
HTML-Modify plug-in to eliminate linked images which can be used as web
bugs (SpamPal and all plug-ins are freeware). Actually, HTML-Modify
simply modifies the HTML tag for images (from <IMG> to <XMG>) which
makes it a bogus tag so the HTML engine doesn't render that code, so you
can still look at the HTML source code for the message to see where the
image would have come from. You could configure HTML-Modify to block
all images and not just the linked ones if you don't want to see any
images in your e-mail which, for example, can speed up downloading of
messages for dial-up users.
If you want a description of how web bugs work, go look at the MsgTag
product (http://www.msgtag.com). This product borrows on the spammers
trick of embedding web bugs in HTML-formatted e-mails. With e-mail
clients that have an option to block linked images, anti-spam products
that will block linked images, or reading in plain-text mode, web bugs
aren't very effective anymore and why it is so very easy to thwart, for
example, the use of MsgTag to determine when someone opens your
HTML-formatted message. I played with MsgTag for about a week to see
how it works but dumped it after figuring out how easy it is to avoid
web bugs along with being an invasion of the recipient's privacy (they
should have explicit permission regarding whether or not they inform the
sender that they opened the sender's message). Some anti-spam products
may actually trigger on the use of web bugs so you benign attempt to
usurp the recipient's privacy regarding notification of reading your
e-mail could backfire and get your web bug ridden message trashed as
spam. Also, using MsgTag has it running as a proxy through which you
send your outbound e-mails and this has MsgTag modify your outbound
message. If you digitally sign or encrypt your message using security
certificates, all your web bugged and modified outbound e-mails will get
reported to the recipient as being corrupted (i.e., they were altered
after being signed or encrypted). The recipient might suspect foul play
and discard your signed or encrypted message as potentially hazardous.
Using the Restricted Sites security zone in Outlook [Express] which is
configured to its High level is sufficient to eliminate any HTML nasties
employed in HTML-formatted e-mails viewed within Outlook [Express].
However, none of the security zones eliminate linked images so web bugs
are still possible unless the e-mail client or a filter strips them out
or blocks them.
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