come out of any chats or messages.. Go to "settings" (bottom right with little cog) click on that. You should see you at the top as "available" with your name, *Emmie* (mines Liam)
Click this, it will take you to a edit profile page
then under the circle near "enter your name and add an optional profile picture" click the tiny "edit" and then pic photo from phone camera
i've just checked my whatsapp groups, my pic doesn't appear either but the others do and from the other side, my pic appears to them. might be the way it works - i don't use whatsapp that much though