If the user has turned images off on his emails, the click through rate will abviously not be very high if you just use clickable images. The click through can easily be increased just by adding text links. to get a reasonable click through rate from these users you should include a short text message along with the images that will interest the user in the images and ensure him or her that you are a source that can be trusted (meaning no viruses, etc in your messages). then you should be able to get a fairly good click through rate (I don´t know the exact percentages, but the click through rate is high enough that many online stores use emails as a marketing tool).
Greetings, sardonicus
