Someone recently asked me “what tools are available to CFers to make one of those dynamic graphic images with embedded text used for requiring a human to read and enter what they see in an input box?”
In this case knowing the name of what you want to do will let you google for it – the name for this is a captcha and google search for “ColdFusion captcha” bring this great blog entry from Christian Cantrell that solves this problem:
http://weblogs.macromedia.com/cantrell/archives/2004/08/captcha_and_col.cfm