I have seen several templates for creating a Google Plus Thumbnail Panorama, but they seem to over-complicate what has to be done. If we go back to the dawn of Photoshop there is a tool that does all the work for us: the slice tool. Using the slice tool to create a thumbnail panorama is as easy as downloading my PSD template – or creating your own PSD that is 670px by 134px with 5 square 134px slices – adding your image (resizing and positioning as needed) and saving for the web.
Gimp:
You can also use the PSD template with the free, open source image editor Gimp. The process does not seem to be as automated, but someone who uses Gimp regularly may be able to correct me on that. Once you open the PSD and add your image to the template, in Gimp’s image menu choose transform and then Guillotine.