That's a great and valid concern. We have studies that show that there is a high volume of people who enable images and thus we would get accurate readings there.

Open-tracking is just one of the features we have, and not central to our entire product. Response-tracking is something that we anticipate more people want to use, and is guaranteed to work in our implementation.

Thanks for the ideas! Stay tuned for our new features that we have planned. We named ourselves EmailOracle for a reason :)