The concept of a "meme" itself (genetic material in media) is at best an analogy to begin with, and from what I've read, fails to take into account the existing literature on semiotics [1]:

Another criticism comes from semiotics, (e.g., Deacon,[16] Kull[17]) stating that the concept of meme is a primitivized concept of Sign. Meme is thus described in memetics as a sign without its triadic nature. In other words, meme is a degenerate sign, which includes only its ability of being copied. Accordingly, in the broadest sense, the objects of copying are memes, whereas the objects of translation and interpretation are signs.

You can go very far down the rabbit hole of pedantry. ;-)

[1] https://en.wikipedia.org/wiki/Memetics#Criticism

I think that's a lost battle, like "hacker".

Words are defined by their usage. A vanishingly small number of people use the term image macro, and in my experience that has mostly been for pedantry.

It mentions the use of video and audio as well, image macros are just the most immediately recognizable