New captcha generation algorithm

captcha/captcha.sh

@@ -0,0 +1,102 @@
+#!/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 + $R % 40))
+
+get_random
+ROLL_X=$(($R % 40))
+
+convert -size 180x60 xc:none -pointsize 40 \
+	\( -clone 0 -fill white \
+	-stroke black -strokewidth 4 -annotate +0+40 "$INPUT" \
+	-stroke white -strokewidth 2 -annotate +0+40 "$INPUT" \
+	-roll +$ROLL_X+0 \
+	-wave "$WAVE1_AMPLITUDE"x"$WAVE1_LENGTH" \
+	-roll -$ROLL_X+0 \) \
+	\( -clone 0 -stroke black \
+	-strokewidth 1 -draw \
+	"line $B1_LINE_START_X,$B1_LINE_START_Y $B1_LINE_STOP_X,$B1_LINE_STOP_Y" \
+	-strokewidth 1 -draw \
+	"line $B2_LINE_START_X,$B2_LINE_START_Y $B2_LINE_STOP_X,$B2_LINE_STOP_Y" \
+	-wave "$WAVE2_AMPLITUDE"x"$WAVE2_LENGTH" \) \
+	\( -clone 0 -stroke white \
+	-strokewidth 2 -draw "line 0,$W1_LINE_START_Y 140,$W1_LINE_STOP_Y" \
+	-strokewidth 2 -draw "line 0,$W2_LINE_START_Y 140,$W2_LINE_STOP_Y" \
+	-strokewidth 2 -draw "line 0,$W3_LINE_START_Y 140,$W3_LINE_STOP_Y" \
+	-wave "$WAVE3_AMPLITUDE"x"$WAVE3_LENGTH" \) \
+	-distort Perspective '0,0,0,0 0,80,0,80 80,0,80,15 80,80,80,55' \
+	-flatten -crop 140x60 +repage -quality 90 -depth 8 png:-
+