Most likely these images are JPEG. Can Abby Fine Reader OCR JPEG images? If so, there would be no need to convert the images to a different format.
If this eBook doe snot have DRM, you can use Calibre with the MobiUnpack plugin to extract the eBook's contents. If it does have DRM, you will need to install the DeDRM plugin.
You can get the DeDRM plugin from
https://apprenticealf.wordpress.com
If you needhelp on how to use the DeDRM plugin, you can do so at the blog where you got the plugin.