In a recent Google+ post, the Gmail team has shared that the even-evolving People Widget will now show recent photos that the person has emailed you. The widget has already had the ability to show contact information and even the person's recent Google+ posts. Now, when you are viewing an email from someone, you will also see a few of the latest images they've sent you via Gmail. Clicking on an image will open up the original email.
This update appears to be a stepping stone. Right now, it appears that the widget will only show you pictures that were emailed to you. In the future, Google could presumably also show pictures the person shared with you on Google+ or Picasa.