So Facebook can't use the thumbs up emoji as a button label any more? Or is that OK because it's an "image", not an "emoji", despite carrying the exact same me

So Facebook can't use the thumbs up emoji as a button label any more? Or is that OK because it's an "image", not an "emoji", despite carrying the exact same meaning as the emoji, and looking indistinguishable from a rendering of the emoji? Or is it OK if they bring their own image file? What if they bring their own emoji font and use that, to improve rendering speed?