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I am seeing an invisible image called cleardot.gif appearing next to the sender's name at the bottom of their email. (immediately to the right after "Sincerely, [their name"]). It only happens with this one person. Where does this come from and what is it?

Here's the code:

< img class=3D"" src=3D"https://mail.google.com/mail/u/0/ima= ges/cleardot.gif" >

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closed as off-topic by Xander, NULLZ, TildalWave, Adnan, Terry Chia Sep 15 '13 at 3:14

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This question appears to be off-topic because it doesn't appear to be a security question. –  Xander Sep 13 '13 at 23:20
2  
If it's not CSS display hack (1x1 pixel images are sometimes required to workaround browser CSS implementation issues); then it is probably a naughty web bug and hence a privacy issue. –  LateralFractal Sep 13 '13 at 23:24
    
Where does it come from? Probably the sender. What is it? Looks like a .gif. –  David Houde Sep 14 '13 at 8:51

1 Answer 1

Probably a form of "read receipt" verification coming from the sender: Has Your Email Been Read? Read Receipts and Web Bugs

To summarise:

If you need to access internet assets (images, etc) in order to view an email, these assets can be personalised for your instance of the sender's email (e.g. [host]/img/message[uuid].png). If you access the image, the sender knows that you (or your software at least) has read the email.

Privacy controls and filter lists within most email clients can block automatic loading of internet assets in an email. The resulting emails might look ugly but at least your privacy hasn't breached.

Note: The fact that the URL in question doesn't seem unique isn't an issue if this is being done by Google on the behalf of the sender (or themselves); as to fetch the HTTPS asset might require your login cookie, which thus links the image request to you.

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