Tracking images in emails

There is some debate on WebMaster world about whether it's a good idea to track if emails are opened using a small image in the email.

There are concerns raised that if an email is tracked, people will mistrust the source, and many people turn off images, so the numbers are not reliable. I would agree with these, but I tracking emails is still appropriate in limited circumstances.

It is important to see if the subject line of the email catches your reader's eye. If one subject line catches the eye of 20% of readers, and another catches the eye of 10% of readers, then twice as many people will ultimately buy your product as a result of the first subject line.

My suggestion would be to send out a pilot of any email to one random sample group of about 50 people with one subject line with the tracking, and another to a different sample with a different subject line. Open rates can be tracked - you should get statistics quickly, and any differences can be noted. You can then send out the email to everyone else without the tracking (possibly in plain text) and you should get a better response rate.