The new app update allows users to long-press the home button and get access to search results based on whatever image or text was on screen at that time. Bing's app also makes sure these searches don't interrupt whatever you were doing when curiosity struck.
Google's 'Now on Tap' does pretty much the same thing — only it's not available for the masses until Marshmallow launches this fall. The only thing that may set these two contextualised search features apart is finding out which search engine is better. Because ultimately, it's Google versus Bing — and the question becomes which search engine can best identify the subject and find the information you want.
For now though, Bing's update is out and we're all curious to see how well it works. While Now on Tap won't arrive until the fall with Marshmallow we assume the functionality will be better thanks to its native build. Still, Google should hope that people don't adopt its rival's useful feature too quickly.