How to add an image to the emulator gallery in android studio?

It's a very old question but I will answer this for future references.

To add any file to emulator just drag and drop the file.

The file will be copied to downloads folder of internal storage.

To access the file

Go to settings

Click On Storage & USB

Click On Internal Storage

Click On Explore (at the end)

and you got it in the downloads folder

now you will get notification to setup virtual SD card, follow the setup. after the successful setup you will be able to see pictures in gallery.