run the following command
adb push <filename> /sdcard
If wanting to transfer all files in a directory onto sdcard, execute the following
adb push <source dir> /sdcard
Then go to DevTools->Media Scanner
Note: you will not see the pics/audio files here when you run Media Scanner.
Now, go to Pictures(Image Gallery). You will be able to see the image you pushed using adb command.
Hope that helps.