Memel

I just have a simple idea on how to protect blogs from spam-bots:

• 1. Make a visible input element for pasting a hash.
  
• 2. Calculate some simple hash of entered post to any visible non-input element within the page.
  a) Calculations may be done on the fly, on each symbol entered into the main content field.
  or
  b) Calculations may be done later right before posting, asking user to wait until calculations done, or even asking user to press some button to calculate it.
  
  
• 3. Ask user to copy this hash and paste it to the input field.
  
• 4. On the server side post must be tested against the hash using same algorithm.
  
• 5. Note: Copy/paste should not be done automatically on submit click!
  

This method, I believe, must be far less annoying for real posters compared to well-known captcha. And it doesn't require any expiration time to be set.