What is it that defines those pixels? How about if you just picked some column, and erased from there to the center of the image, like
[rows, columns, numberOfColorChannels] = size(binaryImage)
binaryImage(:, 50 : round(columns/2), :) = 0;
I don't know if you just want to pick 50 or some other value, basically manually by turning the axis tick marks on and looking at them, or if you can explain somehow how that column could be automatically chosen.