Sprite on mouse-button hold

[Windspar]

1. This is not a pygame event.

elif pygame.mouse.get_pressed()[0]:

You should be using.

elif event.type == pygame.MOUSEBUTTONDOWN:
    if event.button == 1:
        # rest of code.

2. If you can only highlight one image. Then it doesn't belong in a group.

I would need more code or you explain more what you are doing ?
Sound more like a drag n drop.