You can help Google in classifying images. Your efforts will have a direct impact on the performance of Google Image Search.
The regular Google search indexes and classifies web pages based mainly on their text content. Text is relatively easy to process and 'understand' at least in comparison to images. Images on the other hand are extremely hard to understand automatically by a computer without the help of humans. Image processing and comprehension is still a branch of AI that is under heavy research in academic places and in practice needs a lot of resources. For an online search engine to do the same processing on a astronomical number of diverse images present online this requires an unrealistic amount of resources which is not practical, and even then the system will not be fail proof. The only an online search engine can effectively 'understand' images is through the help of humans. By introducing Google Image Labeler, Google is allowing humans to help it classify images found on the Internet. An interesting thing I just noticed today is that Google asks the permission of webmasters to use images in their web sites as content for the Image Labeler. This feature is part of the Google's Webmaster Tools.