Dotcha 🌀

Dotcha is a high-performance Python library for generating captchas based on the Gestalt Illusion principle. It creates visual patterns from thousands of geometric shapes that are intuitive for humans but highly resistant to automated OCR and AI solvers.

Features

• 🎨 Gestalt Illusion: Pure geometric rendering for maximum machine-learning resistance.
• ⚡ High Performance: Optimized rendering (~30ms per PNG).
• 🔄 Animated GIFs: "Temporal Gestalt" effect where text is reconstruction through motion.
• 🛡️ Fuzzy Validation: Intelligent answer verification with Levenshtein distance.
• 🌓 Universal Themes: Light, Dark, and fully customizable color schemas.
• 📉 Scalable Difficulty: Dynamic calibration from clear patterns to chaotic noise.
• 🤖 Async Ready: Native asyncio support for web frameworks and bots.

Visual Examples

Light Theme (EASY)	Dark Theme (MEDIUM)	Animated (Temporal Gestalt)

Installation

pip install Pillow

Quick Start

Synchronous PNG

from dotcha import CaptchaGenerator, Theme

gen = CaptchaGenerator(theme=Theme.LIGHT)
text, buffer = gen.generate()

with open("captcha.png", "wb") as f:
    f.write(buffer.read())
print(f"Generated captcha: {text}")

Asynchronous GIF

from dotcha import CaptchaGenerator, Theme, Difficulty

async def send_captcha():
    gen = CaptchaGenerator(theme=Theme.DARK, difficulty=Difficulty.HARD)
    text, buffer = await gen.agenerate_gif(frames=12)

💡 See examples/bot_demo.py for a complete Telegram bot integration.

Fuzzy Verification

from dotcha import CaptchaGenerator

user_input = "ABCDE"
actual = "ABCD1"

# Accepts answer with 1 char distance
is_valid, distance = CaptchaGenerator.check_answer(user_input, actual, fuzzy_tolerance=1)
if is_valid:
    print(f"Passed! Distance: {distance}")

Why Dotcha?

• Pattern-Based Security: While a human brain naturally connects scattered dots into characters, standard OCR algorithms perceive them as disconnected noise.
• Temporal Signal: The GIF format utilizes "Temporal Sparsity". A static frame is unreadable, but the human eye integrates movement into a clear signal.
• Zero Disk Footprint: Captchas are generated directly into byte buffers, making it ideal for high-concurrency environments.
• Stable & Lightweight: Explicit resource management and minimal dependencies.

Performance

Static Images (PNG)

Difficulty	Time	Shapes	Description
EASY	~0.05s	8000	High density, very clear for humans.
MEDIUM	~0.03s	5000	Balanced density and noise.
HARD	~0.02s	3500	Sparse text, higher background chaos.

Animated Captchas (GIF)

Difficulty	Time (12 frames)	Security Level
EASY	~0.51s	Maximum (High signal integration)
MEDIUM	~0.38s	Standard
HARD	~0.32s	Extreme (Sparse signal in motion)

Note: Timings are based on a standard modern CPU. Generation is offloaded to background threads to keep your bot responsive.

License

This project is released into the public domain under the Unlicense.