Hello I have a static Image gallery (changes are extremely rarely). How long is the maximal time for the Thumbnail cache expiration time?

2. Is it possible to disable rightclick (save image)

I think 120 minutes would be enough.
Right click can only be disabled with external JavaScript scripts.

Is there any way to keep cached state forever (no timeout) so thumbnails not recreated until gallery update?

@ivan

No, there is not such an option. You can set this to a very big value and then clean the cache manually when you update a gallery.