A single php file that generates a transparent image and updates a text file with the number of times it has been accessed. This script is perfect for covertly keeping track of the view count of a CraigsList ad. I created this initially to keep track of jobs and services posts for my business.
Include the script in an image tag on the page you want to covertly keep track of views on. Be sure to provide a unique token for this page.
< img src="http://example.com/index.php?token=CraigsList-ad" />
To view the number of visits, point your browser to the same URL with &show=true added to the end. http://example.com/index.php?token=CraigsList-ad&show=true