I've tried using:
gm convert "source_image.jpg" -fill black -linewidth 50 -draw "line 100,100 100,200" output_image.jpg
But the line that GraphicsMagick draws is 1px wide. I've also tried using 'strokewidth' but the result is the same.
Does anyone know what I am doing wrong? I'm using GraphicsMagick 1.3.16