foyd:
I'm using Arduino Mega, I already made an application in Delphi to / read the webcam, but I wanted to know how the arduino will spend camando to take the picture.
You should be able to extend your Delphi program to receive data from the Arduino. Then it is up to you to decide what the Arduino should send so that the Delphi program knows it should take a picture.
This Python - Arduino demo
should be capable of translation to Delphi - though I know nothing about Delphi programming.
...R