OK, found an example where not every image can be saved:
http://likemag.com/de/6-karten-die-dein-weltbild-komplett-veraendern-werden
The page is in german language, but don't care about that ...
There are several types of images on that page:
1. the picture just below title bar (with the likemag-logo): a right-click opens a menu with the main k-meleon view options (forward, back, reload, save page as, etc.), but no "save image as ..."
2. the main content (the "strange looking" maps): these are just "standard images without link"; a right-click offers the image-menue ...
3. some links with pics (among them videos) in the right column: a right-click just offers the "link- menu", but no pic-save option.
4. more links below the main text (below the facebook-bar): a right-click offers the "link-menu", but this time with pic-save option ...
What's going wrong?