UPDATE: Thanks everyone! I think about 22 people showed up during a game day and got well over the needed img (16 got me the middle badge the previous day).
Tips: best to have multiple things people can harvest on your street, if less people come but do more things it still should work out.
When you visit others make sure to harvest or mine a bunch on each street so it counts towards the img (everything other than animals I think counts). The badges are for 503, 1009, and 2503 total bonus img from the rock.