def mirrorHorizontal(picture):
height = getHeight(picture)/2
for x in range(0, getWidth(picture)):
for y in range(0, height):
topPixel = getPixel(picture, x, y)
bottomPixel = getPixel(picture, x, height - y - 1)
color = getColor(bottomPixel)
setColor(topPixel, color)
color = getColor(topPixel)
setColor(bottomPixel, color)