Typically when my Outlook receives an email it by default blocks all images in it.
However occasionally I get spam emails containing one or more images that are not blocked. An example of this can be seen in the spam email shown below.
Although most of the images in above email were blocked, at least the one with the "Millionaire Blueprint" text was not.
Note that in this case Outlook had not recognized the email as spam. But since it is set to by default to block images in incoming emails, it should block all of them regardless of whether it recognizes the email as spam, or not.
As the images can presumably be used by the sender to validate an email address (or worse), I would like to know what causes a particular image to bypass the image-blocking filter?