Canon EOS M Basic Instruction Manual page 67

If the focus is far off, face detection will not be possible. If you set
[Continuous AF] to [Enable], you can prevent the image from becoming
greatly out of focus.
An object other than a human face may be detected as a face.
Face detection will not work if the face is very small or large in the picture, too
bright or too dark, or partially hidden.
The <p> may cover only part of the face.
When you press the <XL> button, the < > AF point will appear at the
center of the screen. Drag it to move the AF point. Press the <XL> button
again, and the AF point will move to the detected subject.
Since AF is not poss ble with a face detected near the edge of the picture, the
<p> will be grayed out. If you press the shutter button halfway, the subject
will be focused in FlexiZone - Multi method with automatic selection.
When [Continuous AF] (p.72) or [Movie servo AF] (9?) is set to
[Enable]
When [u+Tracking] or [FlexiZone - Multi] with automatic selection is set, the
AF point will be momentarily displayed in the image center if the subject is not
detected. If you press the shutter button halfway, the camera will focus in
FlexiZone - Multi method with automatic selection.
Changing the Focusing Method
67