From Encyclopedia Dramatica
A phrase originating in the Something Awful forums to describe images often used on USENET before the popularization of forums on the internet. An image macro is a photo or picture with a rarely witty phrase superimposed over it, most commonly in white 48pt Impact with a black five pixel stroke. Often used in flame wars and a fundamental feature of gif wars, they convey a humorous message of disdain towards the original poster or the entire thread.
If overused, their impact can be diminished, leading to a lack of lulz. Most image macros suffer overuse within hours of their debut, quickly turning into old memes. 99% of the internets is oblivious to this and will continue using them well past their expiration dates, or until 2012, when the O RLY owl will swoop down and pwn them in the ass.
All you need for a good macro is a hilarious picture with a hilarious caption. Both are needed for the perfect macro. However, if the caption is unfunny, the image automatically becomes fail. If you are a lazy motherfucker, you can have a website do the work for you: See  and 
Image macros have now become synonymous with the unfunny and mass produced, thanks to Memegenerator and all of the stupid faggots in the world that still laugh at fucking terrible macros.
What do they mean?
Sometimes, not always, the meaning of certain image macros is not always clear. They can leave fear, uncertainty and doubt in the minds of the receiving individual. Here is a brief guide to what some image macros mean.
|You have just received this macro:||It means:|
Note: if you receive an image macro of any kind, it most likely means you have been pwned by said macro if not sooner.
|Son of Art/Rosie O'Donnell's fat midget ass on a defamatory macro. Is that teh herpes on the left? Look them little pudgy Republican soccer mom fingers!|
|I'm sorry sir/ madam, but you obviously do not comprehend what is going on directly in front of you so it may help to just sit back and watch for a while longer until you do.|