Preview- move to Trash When opening multiple .jpg files (or other format) I can use the "Move to Trash" on all but the last one standing?

Here is a example of two images, and if I select one then the Move to Trash works.



However if I select all or have only one image showing the Move to Trash is disabled?



My challenge is that I open a group of screen shots and then review and delete.

Let say I have 50 screen shots and I open 10 of them to work with. The names are


Screen Shot 2015-01-19 at 9.14.42 PM
Screen Shot 2015-01-19 at 9.14.17 PM


and so on.  

Obviously I can not remember the specific name once I close the Preview and now have to find and delete a specific one, since now it is a part of larger group with very "similar" names.

Is there a way to use the Move to Trash on all images including the last one standing.
You can move those files directly to the Trash. 


Select them in Preview
Drag them above the Trash in the Dock
Wait for ~2 seconds
Finder window will appear and you can drop those files.


However you won't be able to empty the Trash without closing the Preview window first (the file is still in use).