Canon A1100ISPKIT User Manual (en)

You can change the AF (Auto Focus) frame mode to match the conditions 
you want to shoot.
Select [AF Frame].
Press the 
n button, select the 4 
tab, select [AF Frame], then press the 
buttons to select an option.
Face AiAF
Detects people’s faces and sets the focus, exposure (evaluative metering 
only) and white balance (
When the camera is pointed at subjects, a white frame appears on the 
face the camera judges to be the main subject, and gray frames (max. 2) 
will appear on other faces. When the shutter button is pressed halfway, up 
to 9 green frames will appear on faces on which the camera focuses.
Changing the AF Frame Mode
If a face is not detected and only gray frames (no white frame) appear, 
up to 9 green frames will appear on the areas the camera focuses on 
when the shutter button is pressed halfway.
Examples of faces that cannot be detected:
The camera may mistakenly identify non-human subjects as a face.
If the camera cannot focus when you press the shutter button halfway, 
the AF frame will not appear.
Subjects that are far away or extremely close.
Subjects that are dark or light.
Faces turned to the side or at a diagonal, or faces with a portion hidden.