[FONT=verdana]The first problem that springs to mind is that the recipient’s email reader might be configured to block images by default. That’s not at all unusual. True, you can override that setting, but it inconveniences the recipient if they are forced to do so.
Also, if the image is likely to be large, the email might take a long time to open. And even after it’s opened, it might not fit into the email reader’s window. Plus the recipient won’t be able to change the font size, search for the message, or do many other things that they would expect to do.
On the whole, it sounds like a bad idea. You’re right to be cautious.
Almost half of email is now read via mobile devices. The good news, most of mobile auto downloads images so great creative shows off. The bad news… Big images take longer to load and people are not viewing on broadband all the time.
The real risk to image only email is in delivery rates as there’s nothing for the mail server to grab onto for content. If the email never makes it to the inbox it doesn’t matter what it did or did not look like.
Second to that you have to consider all of the people using Outlook / Gmail / Hotmail [most every desktop user] who will not see anything but an empty box when the email first loads. This isn’t unusual or limited to single image emails… most major senders are pretty graphical… but it’s still a risk.
And finally you have to consider tracking. If the software is just using one image is it adding an open element to that as well?