Create a drop shadow for screenshots using ImageMagic's 'convert'

dropshadow.sh

# add a 1-pixel #777 border and a 2-pixel offset drop shadow of 5 px radius
#
# source: https://stackoverflow.com/a/7136561
function dropshadow() {
    # inner border color and radius
    local ibc=${DS_INNER_BORDER_COLOR:-#777}
    local ibr=${DS_INNER_BORDER_RADIUS:-1}

    # drop shadow color, alpha, width and offset
    local dsc=${DS_DROP_SHADOW_COLOR:-black}
    local dsa=${DS_DROP_SHADOW_ALPHA:-80}
    local dsw=${DS_DROP_SHADOW_WIDTH:-3}
    local dso=${DS_DROP_SHADOW_OFFSET:-2}

    if ! [ -f "$1" ]; then
        echo "ACK! File '$1' not found or unreadable!" >&2
        return 1
    fi

    # slip '-shadow' in between the filename and its original extension
    local of="${1%.*}-shadow.${1##*.}"

    convert "$1" -bordercolor $ibc -border $ibr \( +clone -background $dsc \
        -shadow ${dsa}x$dsw+$dso+$dso \) +swap -background white -layers \
        merge +repage "$of"
}