Images are the "ping" marketers use to track opens. So you'd have an image link back to `http://mysite.com/tracking?email=joe@stuff.com` http://mysite.com/track

Images are the "ping" marketers use to track opens. So you'd have an image link back to `http://mysite.com/tracking?email=joe@stuff.com` http://mysite.com/tracking?email=joe@stuff.com` which will alert them that Joe actually opened the email. This can give them a conversion rate: for the 5000 people we emailed, 230 of them opened the email, and 67 actually followed the link back to the site.