How does Forge decide which card image to use?

Can anybody explain to me how the image file structure works in Forge? I went into the "cards" folder, and there are, what looks like, images for each card, and then many folders with additional copies of the card images in them.
I understand that the additional folders house alternate art for cards from different sets, but when does Forge use these? I updated the images in the main (/cards/) folder with HQ art, but when I go into the game, many of the images are still pulling from the set folders.
Then I tried deleting all of the set folders so the game would only use the HQ images in the main folder, but when I got back into the game, many of the cards images were missing.
Can somebody explain how the game decides which image to use? And is there a way to force the game to only use the "main" image in the /cards/ folder? I don't care about having multiple images for cards. And I don't want to have to update 50 different subfolders with HQ art. I just want to update the main /cards/ folder with HQ art and have the game pull all images from there. Is this possible? Is there an option that says "Don't use alternate card art"?
Thanks for any help you guys can provide!
I understand that the additional folders house alternate art for cards from different sets, but when does Forge use these? I updated the images in the main (/cards/) folder with HQ art, but when I go into the game, many of the images are still pulling from the set folders.
Then I tried deleting all of the set folders so the game would only use the HQ images in the main folder, but when I got back into the game, many of the cards images were missing.
Can somebody explain how the game decides which image to use? And is there a way to force the game to only use the "main" image in the /cards/ folder? I don't care about having multiple images for cards. And I don't want to have to update 50 different subfolders with HQ art. I just want to update the main /cards/ folder with HQ art and have the game pull all images from there. Is this possible? Is there an option that says "Don't use alternate card art"?
Thanks for any help you guys can provide!
