How to Refresh Gallery instantly? I am using Kitkat 4.4.2 on my android device.

When I mount USB drive to my device then all the images,videos in USB drive are shown in the Gallery. After unmounting USB drive, images,videos are still there as a thumbnails.

Can't I refresh my gallery without rebooting?
The system itself AFAIK doesn't expose a GUI element to do so. However, you have multiple options to trigger the Media Scanner:


Reboot the device (not that convenient)
unmounting/remounting the SD card (via Settings; better, but still not convenient)
using one of the apps/widgets available in the app stores. One that's reportedly working with Kitkat is SD Scanner (see my answer here)
using ADB to trigger it (telling it the card has just been mounted – so basically we fake the second option):

adb shell "am broadcast -a android.intent.action.MEDIA_MOUNTED -d file:///mnt/sdcard"

Edit: Some ROMs (e.g. CyanogenMod) seem to have a GUI element for it in Settings › Developer options › Developer tools › Media provider – where you can find a button labeled "SCAN SD CARD"