Here is what you can do as long as these are not browser enabled forms and you dont mind using a small bit of code.
1. Add picture controls for each of the eight pictures and make each picture the default image for that control.
2. Add a 9th picture control that will actually display a picture in the form.
3. In the onLoad event add code to set your main (9th) pictuer control to one of the other 8 picture controls depending on what step in the process you are in. I tried this using a button and rules so it can definitely be done using few lines of code.
Hope this helps!