Say the current item "A" has a link to an image file "A".  The image file "A" will be displayed in the image viewer pane.  Now say I move the focus to item "B", and item B does not link to an image file.  The image viewer continues to display image file A, even though the image viewer was "unlocked".  It would be easy to think that the displayed image A is linked to item B, even though it isn't.  Moreover, if I want to go back to that item A and edit some fields in that item, it's not immediately obvious which item is the one linked to that image.  I may have to look at the name of the image file shown in the image viewer title bar, and then scroll through the grid items until I see that file name appear in the properties pane for the FileName field.  Then I will know I am on the right item that links to that image file.

So here are a couple of ideas to make this easier:

(1) if the image viewer is unlocked, and the focus is moved to an item that does not link to an image file, the image viewer could go blank.

(2) the image viewer could have a right-click option "Return to Linked Item".

I think solution #1 might be better, in order to prevent mistakes about which item is associated with a displayed image - especially since the user can always lock the image viewer to continue to display the same image even though the focus is moved to another item.  Actually a "Return to Linked Item" might be useful in the case of a locked image viewer pane.

Related suggestion - if the focused item links to an image file, but IQ can't find that file (e.g. it may reside on a different computer) - it would be helpful if the image viewer displayed  a "file not found" message, just like the doc pane displays when the file linked in the ItemHTMLFile field can not be found.