It's what is known as an "IM-AGE MAC-RO." Not only is there a picture, but there are WORDS that tie in with the image ("image" is another word for "picture") somehow. [Here, those words are] spoken by a SCOWLING (that's another word for MEAN-FACED) baby.
On behalf of us foreign peasants and non-native English speakers, thank you.
(Though I still didn't understand how a greek prefix became a substantive meaning "place where ceiling cat and basement cat live". But Wikipedia has
an explanation: )
The term "image macro" was first used on the Something Awful forums. The name derived from the fact that the 'macros' were a short bit of text a user could enter that the forum software would automatically parse and expand into the code for a pre-defined image, relating to the computer science topic of a macro, defined as "a rule or pattern that specifies how [who cares]."