gd via the perl API can't read jpg or png

Hi, I'm new to the list.  I have a server on which I'm using GD and the
Perl GD API to create images.  Currently, GD gives a "Problems reading
filename.jpg at scriptname.pl line xx" error when I try to read in a jpg
or png file, but there are no problems reading in gif files.  I would
really prefer not to be limited to 256 colors, though!  I downloaded and
configured a new copy of GD and it found the PNG and JPG libraries
without any assistance, so I have to think that they are already linked
in correctly to the current version.  How can I test this and what can I
do to troubleshoot this problem?

Thanks!

Erin