One of my sites got good traffic from google image search, but as you know the visitors are just interested in images rather than text, and they rarely look at the page content thus effectively neglecting all the adsense ads. The CTR is below 0.2% from them.

Now what can I do to monetize them well? Is it possible with Adsense or should I try something else? Any ideas?

User Google webmaster tool and there is an option to activate it.

Activate what? You mean at https://www.google.com/webmasters/ ?

Activate my adsense ads on google image results pages?

Okay, just checked it out, only an option to opt-in or opt-out some advanced features of image search. How is this going to affect my Adsense image search traffic earnings?