Image viewer for renaming the current image
Solution 1:
Geeqie Image Viewer will do this.
http://geeqie.sourceforge.net/
apt-get install geeqie
or
http://sourcedigit.com/19324-19324/
Solution 2:
XnView Multi Platform will let you rename images "on the fly". Simply click on the file name in the thumbnail view and change the name.
https://www.xnview.com/en/xnviewmp/