Sometimes you need to find the original image on the internet; either to get more information, or to get a better copy of the image. Here are some resources to try.
TinEye Reverse Image Search
ImageRaider Reverse Image Search
You can use an image saved on your computer.
You can search for images you have found online with google.
Search for an image from a website using your computer. On any website, right-click an image and select Copy image URL. Visit images.google.com or click the camera icon in the search box on any Images results page. Paste the URL you copied into the box.
You can also go to images.google.com and drag an image onto the search box. Google may come up with the image you are looking for, or similar ones. Similar ones are sometimes quite useful!