Google Increases Size of Image Database

Although they're just rough estimates that are primarily best used for marketing purposes (aka bragging rights), I guess it's worth noting that Google has just made an increase to the public number they post for total number of images searchable at Google Images. The new total number is 1,305,093,600 images an increase of 117,463,600 from 1,187,630,000.

I would have thought that when Google posted an increase to the total images number it would have been greater than 1.5 billion. Why? This is the number that Yahoo used in an announcement about 4 months ago.