Image Net is a site which has organized more than 14 million images into more than 21,000 different categories and subcategories. So if one searches for the term, 'computer' one gets a list of 26 categories (or 'synsets') that this term may apply to.

If we select just one of these synsets we are taken to a link to hundreds of images which fall in a category and a collapsible tree which shows the particular category's place in the overall hierarchy.

Image Net appears to get better organized results than Google Image search, and it can help you delineate the particular object or concept you want to show a photo of in your presentation or demonstrative.