I can get it so the image top left corner is in the center but I don't want that. I want it so the center of the image is in the center. The screen size will never change from 2560 x 1440 if that helps.
picture = pygame.image.load(images[i])
picture_rect = picture.get_rect(center = main_surface.get_rect().center)
size = picture.get_size()
scale = aspect_scale(size)
picture = pygame.transform.scale(picture,(scale))
main_surface.blit(picture, (picture_rect.center))
pygame.display.update()