Tracker pixels in emails are now an ‘endemic’ privacy concern
Spy pixels, also known as tracking pixels or web beacons, are invisible, tiny image files — including .PNGs and .GIFs — that are inserted in the content body of an email.
They may appear as clear, white, or another color to merge with the content and remain unseen by a recipient and are often as small as 1×1 pixels. Similar pixels are also widely used on web domains to track visitors.
However, according to Hey co-founder David Heinemeier Hansson, they also represent a “grotesque invasion of privacy.”