xmpp/captcha/captcha.sh

#!/bin/sh

# This script is an example captcha script.
# It takes the text to recognize in the captcha image as a parameter.
# It return the image binary as a result. ejabberd support PNG, JPEG and GIF.

# The whole idea of the captcha script is to let server admins adapt it to
# their own needs. The goal is to be able to make the captcha generation as
# unique as possible, to make the captcha challenge difficult to bypass by
# a bot.
# Server admins are thus supposed to write and use their own captcha generators.

# This script relies on ImageMagick.
# It is NOT compliant with ImageMagick forks like GraphicsMagick.

INPUT=$1

if test -n ${BASH_VERSION:-''} ; then
    get_random ()
    {  
	R=$RANDOM
    }
else
    for n in `od -A n -t u2 -N 48 /dev/urandom`; do RL="$RL$n "; done
    get_random ()
    {  
	R=${RL%% *}
	RL=${RL#* }
    }
fi

get_random
WAVE1_AMPLITUDE=$((2 + $R % 5))
get_random
WAVE1_LENGTH=$((50 + $R % 25))
get_random
WAVE2_AMPLITUDE=$((2 + $R % 5))
get_random
WAVE2_LENGTH=$((50 + $R % 25))
get_random
WAVE3_AMPLITUDE=$((2 + $R % 5))
get_random
WAVE3_LENGTH=$((50 + $R % 25))
get_random
W1_LINE_START_Y=$((10 + $R % 40))
get_random
W1_LINE_STOP_Y=$((10 + $R % 40))
get_random
W2_LINE_START_Y=$((10 + $R % 40))
get_random
W2_LINE_STOP_Y=$((10 + $R % 40))
get_random
W3_LINE_START_Y=$((10 + $R % 40))
get_random
W3_LINE_STOP_Y=$((10 + $R % 40))

get_random
B1_LINE_START_Y=$(($R % 40))
get_random
B1_LINE_STOP_Y=$(($R % 40))
get_random
B2_LINE_START_Y=$(($R % 40))
get_random
B2_LINE_STOP_Y=$(($R % 40))
#B3_LINE_START_Y=$(($R % 40))
#B3_LINE_STOP_Y=$(($R % 40))

get_random
B1_LINE_START_X=$(($R % 20))
get_random
B1_LINE_STOP_X=$((100 + $R % 40))
get_random
B2_LINE_START_X=$(($R % 20))
get_random
B2_LINE_STOP_X=$((100 + $R % 40))
#B3_LINE_START_X=$(($R % 20))
#B3_LINE_STOP_X=$((100 + $R % 40))

get_random
RAND_A=$(($R % 10 + 40))
get_random
RAND_B=$(($R % 14))
get_random
RAND_C=$(($R % 10 + 60))
get_random
RAND_D=$(($R % 20))

convert -size 180x60 xc:none -pointsize 40 \
	\( -clone 0 -stroke plasma:fractal \
	-strokewidth 1 -draw \
	"line $B1_LINE_START_X,$B1_LINE_START_Y $B1_LINE_STOP_X,$B1_LINE_STOP_Y" \
	-strokewidth 1 -draw \
	"line $B2_LINE_START_X,$B2_LINE_START_Y $B2_LINE_STOP_X,$B2_LINE_STOP_Y" \
	-wave "$WAVE2_AMPLITUDE"x"$WAVE2_LENGTH" \) \
	\( -clone 0 -stroke plasma:fractal \
	-strokewidth 2 -draw "line 0,$W1_LINE_START_Y 140,$W1_LINE_STOP_Y" \
	-strokewidth 2 -draw "line 0,$W2_LINE_START_Y 140,$W2_LINE_STOP_Y" \
	-strokewidth 2 -draw "line 0,$W3_LINE_START_Y 140,$W3_LINE_STOP_Y" \
	-wave "$WAVE3_AMPLITUDE"x"$WAVE3_LENGTH" \) \
	\( -clone 0 -fill plasma:fractal \
	-stroke plasma:fractal -strokewidth 3 -annotate "2x0+0+$RAND_A" "$INPUT" \
	-stroke plasma:fractal -strokewidth 4 -annotate "2x0+0+$RAND_A" "$INPUT" \
	-roll +$ROLL_X+0 \
	-wave "$WAVE1_AMPLITUDE"x"$WAVE1_LENGTH" \
	-roll -$ROLL_X+0 \
	-distort Perspective "0,0,0,0 0,$RAND_C,0,80 80,0,80,5 80,80,80,55" \
	-rotate "+$RAND_D" \) \
	\( -size 140x60 xc: +noise Random -alpha set -channel A -evaluate set 40% \) \
	-compose add \
	-flatten -crop 140x60 +repage -quality 500 -depth 11 png:-