Consistent top 10 in G image search - but a different 'stolen' version every time!

[Cornwall]

I have a photo that was uploaded back in 2005. It is an aerial shot and has received a fair bit of traffic over the years. I'm pretty sure it was ranked #1 in Google Images for the town name for a while. Now, however, it never ranks.

Well actually it does. But every single time it is a version on a different website that is being used without permission. 
And I'm not talking about one website. Every time I fill out a DMCA and have the image removed only to see a completely different website featuring in the top 10. This has happened 5 times so far and I'm just about to fill out another DMCA request.

What is going on? Surely Google in its infinite wisdom is smart enough to check the timestamp or date cues on page to figure out which is the original. These other sites are often complete unknowns compared to my site which is a 12yr old authority site on the subject.
Don't get it!

[KeriMorgret]

Just to make sure there's not a technical issue, the page isn't noindexed, or you don't have an images directory blocked in robots.txt, correct?