well, if we're going by the original definition of meme as a concept or idea that spreads and mutates like a social version of a gene through a population (Dawkins, The Selfish Gene, 1976), then unfortunately image macros are indeed a form of meme.

also, that's not an image macro. a macro is shorthand; image macros are memetic images, e.g. they have a culturally understood meaning that requires no extra context after learning of it, optionally with attached text that plays off of that cultural understanding. examples of image macros are "foul bachelor frog", "good guy ~~joe~~greg", "hide the pain harold", "this is fine", "all the things", and so on. a comic that sets up a scenario is not shorthand, unless it's "loss" or "sweet bro and hella jeff".

Edit: yes, i'm fun at parties.