Illegal Unit of Measure With xmlto Going to PDF

A colleague created some screen shots using an unknown program that 
apparently has created .png files with only point measurements.  I am 
trying to get these into a PDF document using xmlto.  PDFTex 
complains about illegal unit of measure refering to points and dies. 
I have tried to convert these files to include cm measures, both with 
ImageMagick convert and import, as well as Mac OS X Graphic 
Convertor.  No luck.  Does anyone have any other suggestions?

Harry