It's now possible to run a web search using an image on Google, although the Mountain View crew hasn't really publicized it as yet. This feature works on a basic level by detecting what's in the image. For example, if an image of a flower was uploaded, Google would just search for flowers in general. But now Google has improved this feature by making the search more accurate, so searching for the same flower might yield specific species as well.
Google also added Knowledge Graph to the image search feature. Knowledge Graph was introduced in May, and it adds additional information that it feels you will find useful. For example, searching for "Neuschwanstein Castle" with an image will produce its Wikipedia entry in the search results, and information such as its address, opening hours, and even telephone numbers in the Knowledge Graph area. And if you're using a Chrome or Firefox web browser, images from the Knowledge Graph can be dragged into the search box to start another search.
Source: Google Inside Search Blog