CMigrator can only migrate images that come in the content of the article. We can't deal with galleries or custom gallery codes. If you have that case, then all you need to do is provide the live url link to the wordpress site. Then after the mgiration, you do parsing of the content. AT the parsing stage we remove all wordpress tags that are not supported on a joomla site, look for images in the content and then fetch the images from the wordpress site and add it to your images directory.
Regards,
Daniel