I really like these:
(http://media.galaxant.com/000/091/072/desktop-1415399458.jpg)
(http://media.galaxant.com/000/091/073/desktop-1415399458.jpg)
(http://www.blacksunsoftware.com/pics/illusion/fotito.jpg)
(https://thechive.files.wordpress.com/2014/11/face-art-oleg-9.jpg?quality=85&strip=info&w=600)
(https://s-media-cache-ak0.pinimg.com/736x/27/96/18/279618182c34ea0cc9ca63263d819535.jpg)
(http://1.bp.blogspot.com/-tsPcNblx4bA/UEiJk8RXUTI/AAAAAAAADgw/MiYmHtXCDl8/s1600/hidden_faces_02.jpg)
(https://s-media-cache-ak0.pinimg.com/736x/a9/3e/44/a93e44812798691a5e6e3d18cb7d31ae.jpg)
(http://www.snegidhi.com/images/lifestyle/art/hidden_faces_05.jpg)
(https://s-media-cache-ak0.pinimg.com/originals/45/32/d4/4532d460235a5beaa5c79c4d4a3cb4db.jpg)
(https://s-media-cache-ak0.pinimg.com/236x/55/3d/8f/553d8f691ad51c3e18db48e38d0a9099.jpg)
(https://s-media-cache-ak0.pinimg.com/236x/5a/82/e2/5a82e2fd3b8974f1551fdfa7874d2a44.jpg)