1px by 1px images, what are they?

[pax]

For my HTML affil links it always include a little 1px image, wtf is this?

Also, i want to make it so my adwords ad links to a page that automatically redirects (skip the landing page.) but when im hesistant to a do php redirect cause it doesnt include this 1px image which i have no idea what it does?

excuse the english im drinking

 

[Icecube]

the 1px images are used to track impressions

 

[Kfleming]

If you take the red pill, we continue and you find out what the 1x1 pixel image really is. If you take the blue pill you wake up at home, in your bed and believe whatever you want to believe.