Image Bug
From Market Ruler Help
An Image Bug is a tiny image on a web page which is invisible to a web site visitor, but which communicates information to an alternate Web Server, usually for the purpose of tracking that web site visitor.
ConversionRuler uses Image Bugs to track pages where visitors do not have JavaScript enabled.
The portion of the Tracking Snippet which contains the image bug is this:
<noscript><div style="position: absolute; left: 0"><img src="https://www.conversionruler.com/bin/tracker.php?siteid=XXXX&nojs=1" alt="" width="1" height="1" /></div></noscript>