Step 3: Make an External Button Actuator
If your camera does not have a built-in shutter switch terminal and it is not possible to add a connection to the shutter switch as detailed in step 2, then you still have the option of mounting an actuator onto the camera that can mechanically press the button for you. This will still let you automatically control the camera. It just requires the addition of a motor and a motor controller circuit.
One method is to use a servo to press the button. The servo is mounted immediately next to the shutter button. When the servo turns, the arm (sometimes called the horn) presses the button.
It is also possible to use a regular motor. Just mount it above the shutter switch. Then attach a bracket to the shaft that is capable of pressing the button. You can use something as simple as an offset circle. This method works best for taking pictures at regular intervals such as with a time lapse setup.