From XPUB & Lens-Based wiki

Early web pages used hitcounters as a simple means of collecting what might now be called "analytics". The concept of getting "hits" emerged as the language of web visibility / popularity. (Hit later problematic as site of spamming, relation to search enging gaming)

Notably, early hitcounter's often made use of the fact that a CGI could produce an image as output (rather than just textual / HTML), and thus be placed on a webpage simply with an <img> tag whose src refers to the URL of the hitcounter cgi script.

See wikipedia:Hit counter