Removing duplicate images and videos from Gallery on Samsung Galaxy S4
Go to Settings -> More -> Application Manager.
Under All Applications, select for Gallery app. Now click on "Clear Cache" and then "Clear Data". Follow similar steps for the Media Storage app as well.
Now restart your mobile. Once restart complete, wait for some time so that media service will search for the images, video and other media sources.
Now open the Gallery application, all the duplicate images, videos should disappear.