Dears
can we block only the pics and videos that was used by whatsapp ?
According to Wikipedia:
this.[27]
Multimedia messages are sent by uploading the image, audio or video to be sent to an HTTP server and then sending a link to the content along with its Base64 encoded thumbnail (if applicable).
sounds like all you need to do, is some sniffer work, to see if those images come from the same servers as the communication of the chat