You can do the thresholding or oher image suitable segmentation approach to get the ROI, (preferbly vertical). In that case, you can use the following kernel operation to locate the vertical lines (choose the mask size accordingly)
ker=[-1 0 1
-1 0 1
-1 0 1]
Hope you know how to apply mask on images. This would be more obvious to answer, if you can attach a sample image.
