Reminds me of an anti-crawl mechanism I encountered some time ago in a financial data provider's website: for all numbers in the table, a special font is used where 0~9 are randomly rendered as different chars (e.g. '0' is rendered as 5, '1' is rendered as 8, etc.). The backend server returns the "encoded" chars, and is then correctly "decoded" by the font. The font changes after each reload. So humans always see the correct numbers, but when some crawler uses the HTML source, the numbers are incorrect.