You should check the trash bins for an item.
Found some items by playing myself. But the last drawing is still missing and there is a house across the river. I might have tried going out of bounds with no success for 3 hours... but didn't succeed yet.
You can’t go past the river, it’s there just to tease you!~ ^^
SPOILERS AHEAD
One of the drawings is by the unique yellow flower in the south-eastern part, the second one is in the trash bin by one of the southern houses.
