A tough question after finding kiddie porn

A few weeks ago, Randy Cohen, who writes “The Ethicist” column for the New York Times Magazine, called me to get a better understanding of the sentencing dynamics surrounding the possession of child pornography.  This week’s column has the question that prompted his call: 

I am an Internet technician.  While installing software on my company’s computer network, I happened on a lot of pornographic pictures in the president’s personal directory, including some of young children — clearly less than 18, possibly early teens.  It is probably illegal and is absolutely immoral.  Must I call the police?  I think so, but I need my job.  Signed S.M.N.

Randy Cohen was kind enough to quote me in his answer, though I am not entirely sure I agree with Cohen’s ethical judgment.  I am sure, however, that this is a tough question, and I am interested in reader reactions.