The image is a blackboard, on which a Japanese onomatopoeia called "ざあざあ" in hiragana or "zaazaa" is depicted. This onomatopoeia is used in the situation when it's rainning cats and dogs. There is a good website for learning Japanese language, particularly Japanese onomatopoeia. For it, see my below comment.
This is a completely free image Japanese onomatopoeia-zaazaa that you can download, post, and use for any purpose.
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