Japanese dumb picture threads often start with a request. Maybe someone hasn't laughed in a while and needs a pick-me-up. Thus, he or she asks for silly or stupid pics on 2ch, the country's biggest forum. Others chip in and contribute goofy images to elicit a chuckle or two. Today would be a good day for that.
Or sometimes, funny picture threads appear online with lighthearted titles like, "If you laugh, you must take a bath." Of course, that's a joke, implying that net dwellers never bathe. (They do! Sometimes.)
Then, there are the "complete match" photos, which Kotaku previously posted.