Is there a way to use the built-in webcam with Arduino Uno? I have simply the Arduino Uno and a USB cord, with no other hardware, so I'd like to use my camera built-in on my Mac to take in video input and very simply quantify movements.
An Arduino does not have the speed or memory capacity to handle images or video.
If you have a suitable program on your PC it would be possible for an Arduino to send commands to the PC - for example to tell it to take a picture.
Alternatively, if you have image analysis software on your PC it should be possible to use the output of that to send commands to an Arduino.