The glamour model fears the cage fighter will use her "most intimate photos ever" to get revenge after she dumped him on UK TV after leaving reality show `I`m A Celebrity? Get Me Out OF Here!`.
A source said: "If sleazy photos of Katie came out it would destroy everything she`s trying to do.
"She has just come out of the jungle aiming to reinvent herself as a serious businesswoman and model parent."
Katie`s mother Amy reportedly called Alex`s family to arrange to collect the pictures but her driver was refused entry.
However, the brunette beauty - who raises three children with ex-husband Peter Andre - allegedly has a set of graphic pictures of Alex.
The source added to Britain`s Daily Star newspaper: "Katie took these pictures of Alex for a reason and thinks they are her insurance policy. But he really doesn`t care.
"He`s got a lot of dirt on her and she must be terrified about it coming out and showing what she?s really like."
Katie - also known as Jordan - became the unwitting star of a sex tape when home video footage of her romping with then-boyfriend Dane Bowers was leaked on to the internet and eventually released as a DVD in 2003.