Almost everyone believes they have a decent memory for pictures, and almost everyone is wrong in a specific way. Understanding it makes you noticeably better at every memory board on this site.
Recognition is not recall
Shown a photograph you saw last week, you will recognise it instantly. Asked to describe it from nothing, you will manage a sentence. Those are two different faculties, and the second is far weaker.
A standard pair board mostly tests recognition, which is why it feels easy. A board that shows you a pattern and then hides it tests recall, which is why the same person who clears a twenty-card grid struggles with six positions.
Words are stored better than images
The most effective habit in a memory game is to name each card silently as you turn it. «Blue tractor, top left» is a verbal item with a position attached; a mental picture of a blue tractor is a much fainter thing.
This is why flag and vehicle sets feel easier than food and abstract icons. It is not that flags are more distinct visually — it is that you already have a name for each one, and named things are stored more reliably.
Chunk the board
Working memory holds roughly four items, not twenty. A full grid is therefore impossible to hold as a list and quite manageable as four quarters, each with a handful of remembered positions.
Dividing a board deliberately — and finishing one quarter before spreading out — is not neatness. It is working within a limit that does not move however hard you concentrate.
What this means for the games here
Start on a set whose subject you can name: flags, vehicles, characters you know. Move to food and abstract icons once naming has become automatic, because those are where recall does the work instead of recognition.
And treat the pattern-reproduction boards as a separate skill rather than a harder version of the same one. They are testing something else, and being good at pair boards predicts very little about them.