It would probably relate to the Picasa update because dng [adobe digital negative] .cr2 as my own canon raw files and perhaps other extensions relate to other manufacturer extensions?
i can recognise about three quarters of those extensions and they all relate to image files, so as you suggested some 'image software' is putting them back either through an update or simply when it is used again.
There is a way to keep them from showing in CCleaner if that's what you want to do.
If you right click on an individual entry in the Unused File Extensions list, you have the option to Add to Exclude List.
If you do that, that entry will disappear from the Unused File Extensions list.
If you want to put that extension back on the list, navigate to Options and click on Restore Defaults.
Thanks login123 for information.
However I meant if there is something I can do to prevent reoccurrence of the entries. I know how to hide (exclude) them and I already have done it. I want to solve this issue for good.
agree with @login123, having those entries in the Registry will make diddley-squat difference to any performance indicator.
and the only way to remove them for good is to find out how they are appearing.
if it turns out to be Picasa but you use Picasa then you are between a rock and a hard place.
remove them, run a program until they reappear then decide if you want that program or can substitute it for something else that doesn't go and make registry entries (but they all will, just a question of how much)
"Picasa is software that helps you instantly find, edit and share all the pictures on your PC. Every time you open Picasa, it automatically locates all your pictures (even ones you forgot you had) and sorts them into visual albums ... "
Yes, I use Picasa and the said registry entries were starting to show up only after the latest Picasa update. It's worth noting that deleting these entries makes no problem whatsoever and they are recreated automatically (and found by CCleaner). I have tried it more than twice and no problem observed. So I will keep them in the Exclude List until Google issues another Picasa update which hopefully will resolve this issue because as I said this problem started only after the last update.
Usually when you install image software, there is a section during the installation that asks you to checkmark which file extensions you want to associate the program with. You may try excluding them during the installation and see if that helps prevent the recreation.