by yamachem - uploaded on July 6, 2015, 4:21 am
The image is a blackboard, on which a Japanese onomatopoeia called "がんがん" in hiragana or "gangan" is depicted.
This onomatopoeia is used in the situation when the head is throbbing with the pain after overdrinking alcohol.
There is a good website for learning Japanese language, particularly Japanese onomatopoeia.
For it, see my below comment.