Google Image search is powerful, it helps you find lots of images in a quick and fluid way.
But what about not finding images?
For example, what if you are looking of pictures of navels but not the orange kind, but rather the belly button kind.
You think you can use negative keywords to exclude the word orange from matching in any of the search results. So you'd search for [navel -oranges] and you'd think you won't see any pictures of oranges.
Well, you are wrong - there seems to be a bug in Google Image search where negative keywords have no play in the results you see.
If you want, you can use Bing to search for [navel -oranges] and Bing does a good job filtering out the oranges.
What is wrong, when will it be fixed and if it will be fixed? We don't know.
I do know it was reported by Tristan Savatier (Loupiote) seven days ago at Google Web Search Help but Google has yet to comment or respond. Nor is the issue resolved as of right now.
Forum discussion at Google Web Search Help.
Update: Albert from Google updated the thread saying:
Apologies for not getting back to you. You're absolutely right on the need to add in "-orange" as well. Search won't exclude pluralizations of the words associated with the minus operator automatically. It turns out that the images that are appearing for your initial search are only using the term "orange", without including "oranges".