An active appearance model (AAM) is a computer vision algorithm for matching a statistical model of object shape and appearance to a new image.
[2][3] The approach is widely used for matching and tracking faces and for medical image interpretation.
The algorithm uses the difference between the current estimate of appearance and the target image to drive an optimization process.
By taking advantage of the least squares techniques, it can match to new images very swiftly.
One disadvantage of ASM is that it only uses shape constraints (together with some information about the image structure near the landmarks), and does not take advantage of all the available information – the texture across the target object.