In every browser but Opera 30, I can left-click-drag an image shown in one tab, drag the mouse to a tab with Google Image Search open, and drop the image onto the search field. Google Image Search uses the image as a search term.
On Opera 30, dragging the image to the Google Image Search tab replaces Google Image Search with another copy of the original page the image was dragged from.
Totally broken, no other browser I know of has this issue. FireFox, IE, Chrome, Chromium, Safari, Konqueror (ouch!) all work.