How can I crop an image with Pygame?

You can also use the pygame.Surface.subsurface method to create subsurfaces that share their pixels with their parent surface. However, you have to make sure that the rect is inside of the image area or a ValueError: subsurface rectangle outside surface area will be raised.

subsurface = a_surface.subsurface((x, y, width, height))

cropped = pygame.Surface((80, 80))
cropped.blit(buttonStates, (0, 0), (30, 30, 80, 80))

The blit method on a surface 'pastes' another surface on to it. The first argument to blit is the source surface. The second is the location to paste to (in this case, the top left corner). The third (optional) argument is the area of the source image to paste from -- in this case an 80x80 square 30px from the top and 30px from the left.