Since hold-short lines often
occur in a rectangular window of size 600 by 200 pixels, two
windows are searched, one with (PeakX, PeakY-100) as the
top right corner (left window), and the other with PeakX,
PeakY-100) as the top left corner (right window). The number
of midpoints in these two windows are computed respectively,
and if the count is larger than our threshold of 5 in any of
them, it is determined that hold-short lines are present.