To send images on WhatsApp using PHP, users need to have a Twilio account activated with a WhatsApp sandbox channel and install the Twilio PHP SDK. They must also create a folder named "demo" and copy specific lines of code into a file called "twilioWhatsAppMessaging.php". The code uses environment variables from a ".env" file to authenticate with the Twilio API, allowing users to send WhatsApp messages with image attachments. By following these steps, users can test their PHP application's ability to send WhatsApp messages with images attached, and they can access the full code on GitHub for further development.