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This lovely bit of bat-artwork is by Dave Collinson, and you can buy a print from him for just under fifteen bucks!
In case you’re not familiar with the theme from the 1960s Batman show, which you need to know to get the joke, here it is:
And for those of you who say that there should be eight, and not just four, nanas in the picture, someone on Reddit’s already taken care of that:
Click the image to see it at full size.