On: Gmail blows up e-mail marketing by caching all ima...

[jasomill]

De-duplication does not allow Google to know

    http://marketing.example.com/tracking/some_user.png

in cache is identical to

    http://marketing.example.com/tracking/some_other_user.png

without passing the second URL — a.k.a. the tracking data — to marketing.example.com.