The opening line from the Wikipedia article on the term image macro: "In Internet culture, an image macro is an image superimposed with text for humorous effect."

It is interesting how the term, which originally applied to a function in some forums-software whereby phrases would be replaced with an image. To this day, many chat clients do this with emoticons and some phrases: e.g., in the chat client I use for work, HipChat, "(shrug)" gets replaced by a little ASCII-art picture of a person shrugging.

Many posts on Facebook and other social media are in the form of the newer, extended use of image macro, e.g., LOL cats, etc.

There are some sites where, if you wish, you can choose an image and then type a witty saying, which appears on the image. You can then download or share the image on Facebook, Reddit, etc.

Wow, I have never seen any of those. I'd love to see some of the images.

Look at your Facebook timeline. You won't be able to avoid them!

TV Tropes, of course, has an article.

Dont forget, though, TV Tropes will ruin your life.

Well, I checked my Facebook timeline and found nothing. Nice links, though!

Here's a site for making image macros of the famous British poster Keep Calm.

I love it!

There is just so much to learn...