I have built twelve emoji-mutating machines, each of which changes one characteristic of an emoji—for example, adding glasses, removing a tear, changing a smile to a frown, and so on. Each machine has one and only one effect.
Each of the emojis on the left has passed through the three machines to their right, resulting in the emojis at the right. For example, the smiling, open-eyed, human emoji with a tear (at the bottom left) has passed through machines J, K, and L, resulting in the smiling, closed-eyed, human emoji with a heart (at the bottom right). Similarly, each of the emojis at the top has passed through the four machines below it, resulting in the emojis at the bottom.
What does each machine do?
Note: The emojis at the left and top are semi-transparent because those are the “before” pictures. The machines don’t convert emojis from transparent to solid.
Source: My book (cited here for attribution, not self-promotion), adapted from puzzles by Barry R. Clarke, Challenging Logic Puzzles.