Image sequence mapped to face

I am trying to map a sequence of .pngs to the uvs on the face of my model (so the mouth shapes are created through this projection map).

I got a single .png to work but the sequence doesn’t show. I have the Use Alpha checked but even the preview window shows no image.

What am I doing wrong? I am using this procedure because I want to create a flat cartoon look in combination with shadeless materials.

It should work. could you provide a screenshot of your texture buttons?