How exactly are you trying to replace the image? I ask, because if you are opening the Image dialog and working that way, you will likely lose the connection with image map regions. My own preferred method is to simply work totally behind RoboHelp's back by replacing the image using Windows Explorer. RoboHelp should be none the wiser as long as the file name and location remain the same.
Helpful and Handy Links
Rick, thank you! That worked perfectly -- In my image-editing program to name the new image file with the same name as the previous file, and save it directly to the folder of the previous file, replacing it -- NOT going though Robo's Image processes at all. And thankfully, the new image kept all the image-mapping of the previous file version. A real time-saver!
This is basically what I have done in the past; however since the file was missing "...SHG.gif" in the file name, I was worried that it might not keep the image mapping; but, "no problem," as it did keep the image mapping.