Hi! I just nominated moodboards. In other exchanges, I've seen the 1k equivalent be 3 moodboards, which I agree on as someone who makes them.
The detail within them is dependent on the creator's style, but I think as long as there are at least 4 separate images within each moodboard, it fits the fandom definition. (I usually do 9, but people use varying templates.) If it's any less than 4, it would likely be more in-line with a standard graphic.