Strange things happen Google Image Search

I don’t always figure out how you can optimize for Google Image search. I used to get a decent amount of traffic on my Dutch blog for keywords White Shark (witte haai) or White Sharks (witte haaien). All that traffic was generated through image search.

After the traffic had dropped, I though there might have been less interest in the white shark. The image that I was ranking for was the following image of a white shark jumping out of the water:

I used to appear on the very first spot in image search, and on the top of the normal search, even above the text results. Nowdays, the same image is still there, but it is hosted and taken from another site. They copied the image from my blog and pasted it into theirs. Even the watermark is still there!

Now the question is, how does Google rank images. As it is the same image as before, the one taken from the post: Witte Haaien in het Zwembad. I wonder if they take the most recent image that was published and update their rankings on recency?

So a little test is underway; I wonder if my original post, or either this one will rank back on the position #1 for White Sharks.