MindMyPhone - Photo edition will record photo images when movement is detected by the camera.
Select from options to display a blank screen, a photo or a digital clock while the app is armed and recording.
Choose between the front camera and the rear camera, and an optional alarm will sound if the device is unplugged from the charger.

MindMyPhone-Photo needs to retain the focus to record images and will continue to consume battery power, so it needs to be connected to a power source. It works great sitting in a charging dock on your desk with the screen innocently showing a digital clock or a photo frame.

Note: It may be illegal in some circumstances to record images of people without their knowledge. It is your responsibility to find out if this app is suitable for your situation and to use it appropriately.