Here is what an image would look like before clicking on the #HowOldRobot:
Here is what it would look like after:
This is designed by Bing, hosted at how-old.net. This feature is being experimented with by Bing on Bing Image Search.
When trying this feature myself, I found I could not replicate it after using Bing in both Chrome or in Internet Explorer, although Barry Schwartz stated taht he was able to get it to work on a Windows machine while using Internet Explorer.
The feature was spotted by Venture Beat by way of a tweet from @Fusionfan45.