I tried to prevent my digital photos (.jpg files) from accidental deletion using chmod 444 *.jpg. All permissions are set and displayed correctly in a terminal (ls -la) as well as in thunar's file properties > permissions. The files are displayed with a lock symbol. Even though, whenever I press "delete", the marked file is moved to trash. My expectation was that files without write permission could not be moved to trash. Is it a bug or am I just wrong assuming that moving a file requires write permission?
Actually, Nautilus behaves the same (as does bash terminal). You can delete a read-only file, because it is the directory permissions that control that operation. In theory, you can't write to a read-only file, although many editors will delete the original (or make a backup), then write to a new file, so it seems that you can write to the read-only file.
If you were to make the permissions for a directory r-x, then you would not be able to delete any files (but you could still write to the files, assuming they are not read-only).