feat: Add ability to control color of each character

.gitignore

@@ -9,3 +9,4 @@ testproject/.coverage
 testproject/coverage.xml
 testproject/htmlcov/
 .tox
+.idea

captcha/conf/settings.py

@@ -12,6 +12,7 @@
 CAPTCHA_LETTER_ROTATION = getattr(settings, "CAPTCHA_LETTER_ROTATION", (-35, 35))
 CAPTCHA_BACKGROUND_COLOR = getattr(settings, "CAPTCHA_BACKGROUND_COLOR", "#ffffff")
 CAPTCHA_FOREGROUND_COLOR = getattr(settings, "CAPTCHA_FOREGROUND_COLOR", "#001100")
+CAPTCHA_LETTER_COLOR_FUNCT = getattr(settings, "CAPTCHA_LETTER_COLOR_FUNCT", None)
 CAPTCHA_CHALLENGE_FUNCT = getattr(
     settings, "CAPTCHA_CHALLENGE_FUNCT", "captcha.helpers.random_char_challenge"
 )
@@ -78,3 +79,9 @@ def filter_functions():
     if CAPTCHA_FILTER_FUNCTIONS:
         return map(_callable_from_string, CAPTCHA_FILTER_FUNCTIONS)
     return []
+
+
+def get_letter_color(index, char):
+    if CAPTCHA_LETTER_COLOR_FUNCT:
+        return _callable_from_string(CAPTCHA_LETTER_COLOR_FUNCT)(index, char)
+    return CAPTCHA_FOREGROUND_COLOR

captcha/tests/tests.py

@@ -3,6 +3,7 @@
 import os
 import re
 from io import BytesIO
+from unittest.mock import patch, call
 
 from PIL import Image
 from testfixtures import LogCapture
@@ -210,6 +211,33 @@ def test_repeated_challenge(self):
         except Exception:
             self.fail()
 
+    @patch("captcha.tests.tests.random_color_challenge")
+    def test_custom_letters_color(self, color_challenge_func_mock):
+        color_challenge_func_mock.return_value = "#ffffff"
+        _current_captcha_challenge_func = settings.CAPTCHA_CHALLENGE_FUNCT
+
+        settings.CAPTCHA_LETTER_COLOR_FUNCT = "captcha.tests.tests.random_color_challenge"
+        settings.CAPTCHA_CHALLENGE_FUNCT = "captcha.tests.tests.random_char_challenge"
+
+        challenge, response = settings.get_challenge()()
+        _store, _ = CaptchaStore.objects.get_or_create(
+            challenge=challenge, response=response
+        )
+
+        _response = self.client.get(reverse(
+            "captcha-image",
+            kwargs=dict(key=_store.hashkey)
+        ))
+        assert _response.status_code == 200
+
+        _calls = []
+        for index, char in enumerate(challenge):
+            _calls.append(call(index, char))
+        color_challenge_func_mock.assert_has_calls(_calls, any_order=True)
+
+        settings.CAPTCHA_LETTER_COLOR_FUNCT = None
+        settings.CAPTCHA_CHALLENGE_FUNCT = _current_captcha_challenge_func
+
     def test_repeated_challenge_form_submit(self):
         __current_challange_function = settings.CAPTCHA_CHALLENGE_FUNCT
         for urlname in ("captcha-test", "captcha-test-model-form"):
@@ -549,3 +577,13 @@ def test_empty_pool_fallback(self):
 
 def trivial_challenge():
     return "trivial", "trivial"
+
+
+def random_color_challenge(index, char):
+    return "#ffffff"
+
+
+def random_char_challenge():
+    chars = "abcdefghijklmnopqrstuvwxyz"
+    ret = chars[:settings.CAPTCHA_LENGTH]
+    return ret.upper(), ret

captcha/views.py

@@ -80,8 +80,8 @@ def captcha_image(request, key, scale=1):
             charlist[-1] += char
         else:
             charlist.append(char)
-    for char in charlist:
-        fgimage = Image.new("RGB", size, settings.CAPTCHA_FOREGROUND_COLOR)
+    for index, char in enumerate(charlist):
+        fgimage = Image.new("RGB", size, settings.get_letter_color(index, char))
         charimage = Image.new("L", getsize(font, " %s " % char), "#000000")
         chardraw = ImageDraw.Draw(charimage)
         chardraw.text((0, 0), " %s " % char, font=font, fill="#ffffff")

docs/advanced.rst

@@ -54,6 +54,15 @@ Foreground-color of the captcha.
 
 Defaults to ``'#001100'``
 
+CAPTCHA_LETTER_COLOR_FUNCT
+------------------------
+A string representing a Python callable (i.e., a function) to determine the color of the letters in the CAPTCHA.
+
+Defaults to ``'None'`` (uses CAPTCHA_FOREGROUND_COLOR) for all letters.
+
+This function is called for each letter of the CAPTCHA string.
+It takes two arguments: the first is the index of the current letter, and the second is the entire CAPTCHA string.
+
 CAPTCHA_CHALLENGE_FUNCT
 ------------------------
 
@@ -298,3 +307,4 @@ This sample generator that returns six random digits::
         for i in range(6):
             ret += str(random.randint(0,9))
         return ret, ret
+

testproject/helpers.py

@@ -0,0 +1,16 @@
+import random
+
+
+def random_letter_color_challenge(idx, char):
+    # Generate colorful but balanced RGB values
+    red = random.randint(64, 200)
+    green = random.randint(64, 200)
+    blue = random.randint(64, 200)
+
+    # Ensure at least one channel is higher to make it colorful
+    channels = [red, green, blue]
+    random.shuffle(channels)
+    channels[0] = random.randint(150, 255)
+
+    # Format the color as a hex string
+    return f"#{channels[0]:02X}{channels[1]:02X}{channels[2]:02X}"

testproject/settings.py

@@ -79,4 +79,5 @@
 CAPTCHA_FLITE_PATH = os.environ.get("CAPTCHA_FLITE_PATH", None)
 CAPTCHA_SOX_PATH = os.environ.get("CAPTCHA_SOX_PATH", None)
 CAPTCHA_BACKGROUND_COLOR = "transparent"
+CAPTCHA_LETTER_COLOR_FUNCT = "testproject.helpers.random_letter_color_challenge"
 # CAPTCHA_BACKGROUND_COLOR = '#ffffffff'

testproject/urls.py

@@ -10,4 +10,7 @@
 from .views import home
 
 
-urlpatterns = [url(r"^$", home), url(r"^captcha/", include("captcha.urls"))]
+urlpatterns = [
+    url(r"^$", home),
+    url(r"^captcha/", include("captcha.urls")),
+]