Move the pointer left and right across the image to change its position. This program overlays one image over another by modifying the alpha value of the image with the tint() function.
offset = 0
easing = 0.05
def setup():
size(640, 360)
global img
img = loadImage("moonwalk.jpg") # Load an image into the program
def draw():
global offset
image(img, 0, 0) # Display at full opacity
dx = (mouseX - img.width / 2) - offset
offset += dx * easing
tint(255, 127) # Display at half opacity
image(img, offset, 0)