This plugin creates a resistor color code captcha on comment forms
This plugin will draw a random 5% or 10% resistor and four color band sliders beneath it. The commenter needs to match the colors on the sliders to the colors on the resistor.
Commenters don't actually need to know how to read resistors.
Random resistors are generated from E12 and E24 decade values (so there's never something like a 4.6K Ohm resistor).