Detection Framework

JSteg detection:
Simple, similar to Westfeld and Pfitzmann.

JPHide detection:
Re-arrange DCT coefficients according to table.
Ignore modifications to 1, 0, and -1.
Ignore modifications that are not LSB.

Outguess detection:
Not that easy.
Uses sliding chi-square test with adaptive sample size.

Accuracy and performance enhancements:
Sample size is adapted by binary search.
For JSteg and JPHide, test stops once probability falls below threshold.
For Outguess, ignore certain coefficient combinations.