Personally I don't understand the sense to have categories, today.
At first there is a big lack of categories and most of the time the images don't really fit in one.
Then I am not sure that customers use categories in their research (I am almost sure they don't). In fact when a customer is looking for an image he perfectly knowns what he wants. And if he searches by category he will get 1 000 000+ images, and 90% of these images will absolutely not correspond to what he is looking for. So, if he need a photo of a "blue banana" he will surely not look in category "fruits" or "food" (and which one is the right one, as a banana is a fruit and a food too?), but he will directly enter the keywords blue + banana.
So why to "annoy" contributors with categories (a big time wasting)? (In most of the most new image banks they stopped to use)
Nikon D610 - Nikon D300 - Sinar P3 and Hasselblad H2 with Sinarbacks