Most don't really post actual black and white images, choosing to use instead a convenient phone app.
Mahala decided to add her own twist to the challenge - opting instead to do her own black and white illustrations.
Here are a couple.
This last one is not a drawing but a photo Mahala took - Fine China by Anatomy Boutique @anatomyuk for #WellcomeBlackwell shop, #AnatomyofDigestion.
We've included it simply because it's black and white-ish too.