From wikipedia, Ema (絵馬?) are small wooden plaques
on which Shinto worshippers write their prayers or wishes.
The ema are then left hanging up at the shrine,
where the kami (spirits or gods) receive them.
They bear various pictures, often of animals or other
Shinto imagery, and many have the word gan'i (願意),
meaning "wish", written along the side.
All photos are from Tokyobling's blog, see all detail there.