If you are a Gmail user you have probably gotten the popup upon login that images are now enabled by default. This coincides with Gmail announcing a couple of weeks ago that they will be caching and serving the images from their CDN to speed up browsing email.
You also have a option to disable this in your settings to go back to the “Ask me before displaying” just like the old Gmail setup.
Personally, I feel this is a new spam signal that Gmail will use to adjust their already great spam detection system.
The biggest single problem that Gmail has with spam is mass mailers (spammers) Â is using 100% images that contain keywords that would be flagged as spam. Â I am guessing they are trying to OCR (optical character recognition) but that is a monster in itself.
Also these spammers get around easy detection systems by sending from a slew of different IP addresses, Â subject lines, Â alt tags for images, and other items.
By caching these images Gmail can now use that as a signal when enough people report the email as spam and either not display the image, Â flag all emails with that image as spam, Â or even replace the image with a “this is spam” or something.
Many people have written various theories on this but only time will tell how its going to be implemented.