You are going to need to modify how/where your Kobo scans for files. If you use the OCP install script, it will make the change to your Kobo eReader.conf file otherwise open Kobo eReader.conf and look for the [FeatureSettings] header. If that is present add the ExcludeSyncFolders line, if it is not present, add both the FeatureSetting and ExcludeSyncFolders lines.
Code:
[FeatureSettings]
ExcludeSyncFolders=\\.(?!kobo|adobe).*?
Please note that adding this line will cause your Kobo to delete any files that it's added to your library from a folder that is now excluded. This will require you to re-install third party apps (KFMon, Plato, etc.).
The Kobo eReader.conf file lives in the .kobo/Kobo directory and, if you are using Windows, must be edited with a end of line sensitive editor (my choice under Windows is Notepad++).
If you want to check out the OCP, see the
One-Click Install Packages for KOReader & Plato thread. The script links are in the second message in that thread.
Lastly, use the Paperclip tool or the Manage Attachments button in the Attach Files box to keep from violating forum rules on maximum image size.