Have recently upgraded from 1.8.10 to 2.0.0 and the 2.x new images were not automatically installed.
Have ran the png_to_xml.sh script to create the xml file containing the new images and then tried to import using only Update Images and Add new Images from the import form.
Although got an Import Successfull message, no new images were present.
When retrying and leaving all default options selected on the import and also including maps (update/add), the images were imported successfully.

Not sure which "tick" option helped it to work, but I'm guessing it should have worked by only selecting images and nothing else.