Well, as required by the Google+ profile pictures wall design-template,
the image needs to be sliced to 5 times 128×128 pixels – with a padding of 20 pixels.
This is how it looks in GIMP:
…and this is how it looks online (a screenshot of Google+ in German):
Of course one doesn’t need to use a single fragmented background image —
fitting individual images work well, too.
The attached zip-archive contains the .XCF template which I used for slicing: