It is not obvious the 'image-icon' is in fact the lightbox function. (...) I am absolutely sure a large part of my member-base will find these things confusing.
Thinking about this image-icon which represents (at least one of the different meanings) the lightbox function in the XFMG: why do we even need it? Because we already enter the lightbox mode the moment you click on an image. It works the same in XF (forum): when you click on an image in a forum-posting, you enter the lightbox mode. Without any need to click a separate button first. Maybe it's because of the video's:
There is a difference between the lightbox in XF (forum) and XFMG: it seems that the lightbox in XF does not included posted videos in it (I do not know if this is an ACP setting), whereas the lightbox in XFMG
does. (another inconsistency (?> maybe it's a setting) because of the fact that 2 different lightboxes are used in different products)
So, if you only have videos in your album and you want to see them in the lightbox, you need a separate icon. Because clicking on the video,
plays the video, instead of opening it in the lightbox (as it works with pictures).
Anyway, the lightbox on videos has the benefit of being able to scroll through all your video's easily, without having the need to click on the <- and -> icons in the menu (next to the lightbox icon), which makes scrolling much more cumbersome, since it's refreshing the 'entire' page everytime you scroll to another video/pic.