how to make certain pixel values = 0 or 1

i have an image where in i have to detect duplicate regions. i compared the feature vectors of image blocks. now based on certain condition i want to make certain pixel vales black or white. i have the location of pixel values. please help me to mark certain pixel values to white or black.

[Massimo Zanetti]

What the condition?

[Jan]

You have the location of the pixels already? In which format?