First, it isn't normal behaviour (default action for file system shield) for avast to scan the folders contents when you open it. avast is an 'on-access' scanner so something is accessing those files to cause avast to scan the contents. That is why I mentioned the ZbThumbnail.info as I don't know what that is meant to do as I don't have a Cannon camera nor the software to see what it does.
So that is the quandary, as avast doesn't initiate scans, but reacts to something accessing the file or you have changed the default settings in the file system shield (and I believe you said that you hadn't in an earlier post).
Second, what Exclusions did you use as the avast Settings, Exclusions are effectively for the on-demand scan and these are being scanned by the on-access scanner (file system shield, expert settings, exclusions).
However, I wouldn't advise excluding complete folders or just file types (e.g. *.jpg) within a folder as there are image file types , which can be exploited/infected so they should be scanned on-access.
Whilst doing this I have opened 17 image folders/sub-folders and the file system shield started with an activity count of 822 ending 939. There are many hundreds (I didn't count them) of images in those folders and only on the odd occasion did avast actually scan a file in the folders, one time it scanned a thumbs.db file that it left behind.
Most of the files scanned were through my use of image capture software to grab some basic images (the creation of a new file, etc.) and only a few images were actually scanned outside of that, why I don't know as I wasn't physically accessing a file in the folder/s. So it is still a mystery to me why it is scanning your files.