The Python Imaging Library (PIL) allows image processing in Python. To change an image color to sepia, first import the Image module from PIL. Open the image using Image.open(). Then, create a sepia filter by defining a function that takes an image and returns a new one with sepia tones. This function should iterate over each pixel in the image, get its red, green, blue values, calculate new RGB values based on standard sepia formula: R = 0.393*r + 0.769*g + 0.189*b, G = 0.349*r + 0.686*g + 0.168*b, B = 0.272*r + 0.534*g + 0.131*b. If any of these exceed 255, set them to 255. Finally, use putpixel() method to apply new RGB values to each pixel.
