Spy pixel

Spy pixels or tracker pixels are hyperlinks to remote image files in HTML email messages that have the effect of spying on the person reading the email if the image is downloaded. They are commonly embedded in the HTML of an email as small, imperceptible, transparent graphic files. Spy pixels are commonly used in marketing, and there are several countermeasures in place that aim to block email tracking pixels. However, there are few regulations in place that effectively guard against email tracking approaches.