"New Blog Templates"Plugin Screenshots are all the same

I made four modifications to the Twenty Twelve templates and set them up in the "New Blog Templates" plugin. When displaying the Screenshots for new user selection it displays 4 identical screenshots of the generic Twenty Twelve template without any mods, just different Titles and Descriptions, so visually, nothing to choose from.
Is there anything that I can do to display the modified screenshots, and if I have to do this manually, can you provide instructions?