What's the point of a 1px height image provided by Affiliate program?

Question

I am looking into some html provided by an advertiser that we would like to link to, and it has a strange image included at the end of the html code:

<img src="http://www.<some domain>.com/image-<some numbers>-<some numbers>" width="1" height="1" border="0"/>

What is the point of this? Is this to count impressions?

Answer 1

Additionally, those "numbers" may represent unique data like affiliate ID or may be unique to your site. So, when a browser requests the image, the server may set a tracking cookie that gets your site or the affiliate paid for any eventual purchases on the advertiser's site.

This is totally harmeless at worst and could be profitable at best.

Answer 2

Yeah, each load of the page will fetch that image too, so their log will include the time and ip address so they can count the impressions, graph the uniqueness, etc.