Canon POWERSHOT A1100IS User Manual page 76

You can change the AF (Auto Focus) frame mode to match the conditions
you want to shoot.
Select [AF Frame].
Press the MENU button, select the O
tab, select [AF Frame], then press the ,q_
buttons to select an option.
Face AiAF
Detects people's faces and sets the focus, exposure (evaluative metering
only) and white balance (AWBonly).
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.
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