Q:

How to detect an 'image area' percentage inside an image?

Mhh, kinda hard to explain with my poor english ;)
So, lets say I have an image, doesnt matter what kind of (gif, jpg, png) with 200x200 pixel size (total area 40000 pixels)
This image have a background, that can be trasparent, or every color (but i know the background-color in advance).
Lets say that in the middle of this image, there is a picture (for keep the example simple lets suppose is a square drawn), of 100x100 pixels (total area 10000 pixels).
I need to know the area percentage that the small square fill inside the image.
So, in i know the full image size and the background-color, there is a way in php/python to scan the image and retrieve that (in short, counting the pixel that are different from the given background)?
In the above example, the result should be 25%
EDIT: this are two image as example (gimped oin the way ;):

I need to know the percentage of the green pepper in the whole image (that is 400x400)

A:

from PIL import Image
image = Image.open("pepper.png")
bg = image.getpixel((0,0))
width, height = image.size
bg_count = next(n for n,c in image.getcolors(width*height) if c==bg)
img_count = width*height - bg_count
img_percent = img_count*100.0/width/height

gives 7.361875 for both images

