Opens are actually calculated by a tracking pixel which is an image, so technically, that is measuring whether or not your recipients have images enabled for a particular mailing. Also, if you are wanting to track the clicks of a particular image, then you will need to have that link out to something.
For more information on response data and how it's measured, take a look at these articles from the Emma Resource Center and just let me know if you have any additional questions. - Thanks!
It is interesting to know how an email open rate is determined. I never knew that was the process.
What I am looking for though is the rate that people open or download the images in an email after they have opened the email.
If I receive an email in my inbox and I open it, I am then looking at a screen with some copy and some frames. Sometimes the frames have alt text and have links and sometimes they don't. For the purpose of this question, it doesn't matter whether the frames have alt text/links or not. They remain frames until I actually go to some part of the email and click "download images" or something of that nature. That is the rate I want to know, of the people who have already opened the email I sent them, how many actually opened or downloaded the images. Perhaps I should have asked for the rate of people who download an email's images.