"By many different people" isnt part of either of the above definitions. Also, whats "many?" Whats "different" mean in this context? What is the threshold for a meme to meme? 10 people? 100? 1000?
Richard dawkins coined the term in 1976 and defined it as such:
A meme “conveys the idea of a unit of cultural transmission, or a unit of imitation”
Seems like a screenshot of text seen by hundred/thousands/millions fits that defention to me.