In order to access the Picture or Video Message that you received the message about, you will first need to login to the My Verizon account for your mobile number. You are able to login by going to this link:
If you have trouble logging in, you can go through the Password Reset process via the following link:
Once you are logged in, you will place your mouse over Messaging and then select Send Picture and Video Messaging. You will then select Messages to view messages sent to you.