A picture of yourself on Voice mail?
Well it would be the same as adding photos to other contacts (like family and friends)
simply open the dialer app or contacts then go to contacts ... for Voice mail Go to V and look for Voice mail, press it then tap on the generic picture to change it... now for texting yourself.. On the top there's a "set up my profile" in the contacts section. Set that up, change your picture and tada~
If you already did that before look for your name in the contacts or number then change the picture