tl;dr: Decoy Font is a downloadable TTF font that exploits the hybrid image technique (same idea as the Einstein/Monroe illusion), overlaying sharp foreground letters on blurred, low-frequency background letters so humans reading from a distance see a different message than what AI/OCR sees up close. The author demonstrates it fooling ChatGPT and Gemini 3.5, though notes agentic models with proper prompting could likely defeat it. It's positioned as an accessible anti-AI-scraping tool, with potential applications in CAPTCHAs or private messaging.