~ always means “user home” as in
/home/pi/ = ~
so, on the pi your home is probably
/home/pi
so ~/.emulationstation is
/home/pi/.emulationstation
where the . says its a hidden directory so type
$ ls -al
and you’ll see it listed
but you don’t have to list it to know its there and goto it, you can just type
$ cd /home/pi/.emulationstation
which will take you to the place where downloaded_images is located.
the game images are by default placed into
/home/pi/.emulationstation/downloaded_images/system
so for Hudson Island (NES?) it would be
/home/pi/.emulationstation/downloaded_images/nes/adventureisland-image.jpg
but, this is only where the scraper sends the images for its library
the real culprit is in gamelist.xml for that particular system
so, view the gamelist.xml in that system, which is located in /home/pi/.emulationstation/gamelists/nes/gamelist.xml
$ nano /home/pi/.emulationstation/gamelists/nes/gamelist.xml
will open the file, and you can edit it. find the corrosponding <game> tag, and you can change the file it pulls for the artwork with ease, to whatever directory you’d prefer