Most photos on their own aren't funny, adding text makes photos funny or gives them context when it's unclear what the photo is about.
How many photos have you seen and wanted a caption to explain the photo? Probably most photos.
Memes condense universal ideas that most people are familiar with and usually make a point better than typing lengthy explanations.
Shortened abbreviated language is the future, it will probably be called Newspeak or Internetspeak or Shortspeak ...
"If we want to talk about how many words there are in English, there are three key numbers to remember: more than a million total words, about 170,000 words in current use, and 20,000-30,000 words used by each individual person."
Over 80% of words could be removed from the dictionary and most people wouldn't notice or care.