Google have improved image search quality. (launch codename “endearo). They are ranking pictures from authority websites higher than pictures from websites with less authority, image search is huge, so be sure to name your image files with your keywords, use Alt tags and captions (As below).
Once again, this is an expected development within Google. It makes perfect sense to have the pictures ranking from the best quality websites. So get focused and develop quality sites.
With search engine optimisation, video, picture, audio, pdf, text, etc, should all be used and try and go for quality over quantity, because the search engines are getting smarter and the eventually, the cream always rises to the top:)