I don’t think it’s exactly a meme as such, but a sort of meta that works on apps and platforms where images are cropped down to square(ish) thumbnails.

On those platforms you’d only be able to see the middle part of the image with the"tap me" text, which is positioned carefully in the vertical center such that it will be visible in the thumbnail. And on tapping/clicking, you reveal the rest of the image for the ‘surprise’

I think Lemmy web does crop, but on my Lemmy app the whole “thumbnail” is shown in my feed even as ridiculously tall as it is, so the “tap me” thing is meaningless since I can see it already.

On the converse in fact, Lemmy seems to have a bit of a meta itself where people have at times posted outrageously long and tall images intentionally because they take ages to scroll past on your feed - which works only because some Lemmy apps do NOT crop.