How to send images from pc to android automatically through USB?

Once you connect your phone to a PC, you can access the phone memory from your explorer; we are talking here in term of MS Windows OS.

using ddms

http://www.moncefbelyamani.com/how-to-take-a-screenshot-of-your-android-device-using-ddms-on-a-mac/

Sending by using different mobile syncying applications like moborobo

or you can see what are the options on the dialog: choose what to do when the device is connected to pc