There are several ways that you can start a search of this type, but I think the easiest is to go to images.google.com and click on the small camera icon on the right of the search bar. When you do so, you’ll have the option to either upload an image from your computer or paste in the URL of one.
If you’re using Chrome or Firefox, you can also drag an image right from the Finder and drop it onto that box to begin searching.
As you can see below, when I searched for a picture that I took, Google returned results with visually similar images since it couldn’t find an exact match. This may mean that the pictures are of different subjects, but the colors, angles, and other elements match closely.
If you look at the screenshot I took when I added a search term, though, all of a sudden I have photos that were taken not just at the same place where I took mine, but ones that are almost exact duplicates of my original image.
For more information about this latest triumph of Google technology, visit their Search by Image help page. From there, you can also download the Chrome or Firefox browser extensions, which allow you to right-click an image on the Web to start a search. Really, this kind of stuff makes me salivate just a little bit.
Right-clicking on an image with the Chrome browser extension installed results in a bag full of awesome.