Pixel Stuffing

A form of ad impression fraud, pixel stuffing is when one or more ads are served in a display unit the size of a single 1×1 pixel.

According to the ad server, the ad has been delivered on the web page, so an impression is counted that the advertiser pays for – but the reality is that the ad is so small it can’t be seen by the user, so there is no chance of them engaging with it.