use imagemagick convert to generate screenshots with drop soft shadow effect
# TODO: add text
#
$ convert -page +8+8 small_gsc_screenshot_20041019.png -alpha set \( +clone -background navy -shadow 64x8+8+8 \) +swap -background none -mosaic small_gsc_screenshot_20041019-shadowsoft.png
# example result: https://github.com/mbohun/gtk_shader_ide/blob/master/doc/small_gsc_screenshot_20041019-shadowsoft.png