About this question
To stego detect images, it really comes down to statistical analysis (not a subject I know very well).
But here are a few pages that may help you out.
Steganography Countermeasures and detection - Wikipedia page worth a read to cover the basics.
An Overview of Steganography for the Computer Forensics Examiner - Has quite a long list of tools and some other useful information.
Steganography Detection - Some more information about Steganography.
Steganography Detection with Stegdetect - Stegdetect is an automated tool for detecting steganographic content in images. It is capable of detecting several different steganographic methods to embed hidden information in JPEG images. Tool hasn't been updated in quite a while but it was the best looking free tool I could find with a quick search.
