[plehoux]

The UI confusion come from the shadow projected on the selected thumbnail. If the thumbnail is located in a dark region of the picture, the shadow become invisible, it's thus impossible to quickly recognize where we stand in the thumbnails stack. The horizontal translate is too small to compensate.

You could draw a small white circle with black shadow under the selected thumbnail, or simply swap the thumbnail for a white circle when it's selected.

I think the thumbnail are also to small, we cannot easily distinguish details by looking at them, so they serve no purpose.

Great pictures.