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Although GIMP is a fantastic image editing tool, it's not what you need for simply view images. For some reason, it came installed with Crunchbang set as the default image viewer, instead of the lightweight gpicview.
To set gpicview as default image viewer - simply right-click an image file in your file manager window, and select “open with gpicview”. From there, click the preferences icon on the bottom right and select “Set gpicview as default image viewer”.
(machinebacon) viewnior is the default image viewer. [outdated]