@WaltWM . . .I'm just guessing but your image problems might be caused because your images were in base64 binary format(instead of being link referenced in jpeg format) when you converted to epub. For instance, I know that it is certainly possible to save all doc images in base64 binary format when you save your doc in LibreOffice Writer or OpenOffice Writer for instance.
Base64 format just saves the images in full binary format within the epub html itself. Of course, saving images like this is quite messy and not really in accordance with the epub standard. So it's not that surprising that base64 binary format is usually disallowed in favor of referencing your image directly from within the
Images dir in the epub. In html, base64 binary format looks like this(see Spoiler):
Whereas an acceptable image that has been properly added and referenced from the epub's
Images directory, looks like this:
<p class="center"><img style="width: 25%;height: auto;" alt="My image" id="My_Image" src="../Images/my_image.jpg"/></p>
Really, using Sigil, what you need to do is just check that your images have NOT been saved and inserted in base64 binary format within your epub. I would simply use Sigil to inspect your epub images within the relevant xhtml files your epub. And if they are formatted in base64 binary format I would simply delete them from the xhtml and then add those same images back into your epub's
Images directory. Finally, you should be be able to properly insert your ebook images as acceptable referenced images into your xhtml file by clicking
Insert > File using Sigil(free epub editor). But if you are adding a cover image -- you should click
Tools > Add Cover to add your cover image.