this extension as is, even if 100% working, secure and fast, will be never be validated, even if it works perfectly, and in the respect of the other extension below mentioned (that finally i was able to install and see what it do and how, so little sorry for answer below), is less intrusive, more immediate, preserve gif transparency, and resolve the cache images issue
(images rendered immediately after rotated on page).
It has been asked to take a look on the other ext, improving on it some aspect, and may moving features of this extension into it. I'm sorry, i will not follow, i will continue following with this, for reasons mentioned above:
It will be ever available there, and improved time by time.
The rotation popup css/html customization will be the aspect that will be added soon, and for that will be easy to play with for anyone.
Then adjusting something else more on code to accomplish with phpBB code rules, finally may presented for validation (then it will be available under extensions here at phpBB.com).
This post can be moved, split or even removed.
Just remember that if you want the result that you see possible with this extension, you have to download it from github at moment.