Originally composed solely of a series of images by Ayakashi showing the girls of Gensokyo confessing their romantic feelings to the viewer. This pool now includes any solo image of one of the characters of Touhou confessing their love to the viewer.
Taken from the pixiv images tagged 東方告白祭り
...though not necessarily limited to that tag grouping.
For images where the girl is receiving the confession, please see pool #1193, "Touhou - Love Confessions in Gensoukyou".