The Mask can be found in the prison level, In the socond cell block with 3 guards patrolling it. If you sneak behind the guards, fallowing the guars counter clockwise. You will find the key behind the second pillar. Now the first door you see(northeast) open it and smash the picture on the shelf. The Jak Mask is now yours.
Sly Cooper Mask
The Sly Cooper Mask is in the City Port area. There is a box behind the warp gate to Emerald Isle that you can jump onto. Jump up on it, then go behind it and turn back the way you came. You will see the back of the box has a picture on it. Smash the picture, then go inside the box. Inside is the Sly Cooper Mask.
Human Daxter Mask
The Human Daxter Mask is in the Hotel Level. After the first pipe slide, you run up a slope. When you get to the top, trun around. You should see a ledge. After you get the Flamethrower attachment, you can reach it. On the ledge is the picture. Smash it, and You get the Human Daxter Mask, and the Hat.
The Samos Mask is in the Lumbermill stage. After the first bug zapper, you have to pass a few saw blades. After that , if you look to your right, you'll see a tunnel with a saw blade in it. Look towards your left. You'll see a stream. Jump off the platform to your left, and hover, staying close to the wall. After a few seconds, you'll come to a small space in the wall. Inside is the picture.Smash it, and you get the Samos Mask.
The Ratchet Mask is in the Subway level. After the part where you jump from train to train, you'll come to a section where you have to climb up some net, while avoiding the energy going up it. When you reach the top, look down the side closest to the entrance to next part of the level. Drop down onto the ledge, smash the picture, and you get the mask.
The Clank Mask is in Tanker 1. After Several of the spring pads, you have to climb up a wall. When you get to the top, turn around. there's another wall you can climb. Hover over to it, climb it, then turn around again. You'll see the picture on the ledge across from you. Hover over, then smash it.