strip_image_tags not working

[eluser]Neil_W[/eluser]
Hello,
I'm getting this error in my form validation:
Call to undefined method CI_Input:trip_image_tags()

However, my set_rules is configured as follows:
xss_clean|strip_image_tags

I am loading the Security helper and there are no errors with xss_clean call, and if I add encode_php_tags or any other method in the Security helper I get no errors, it's only when I add strip_image_tags.

Any help would be appreciated.

Also, a quick question on xss_clean: does it simply check for xss or does it apply any manipulation such as stripping html tags, etc.

Thanks.