Thanks again, Wysota, I got your test program to work now.

The computer that does not have Qt4 recognizes bmp, pbm, pgm, png, ppm, xbm, xpm as image files. The list is not getting longer when I put all the Qt image dll files in the "imageformats" folder.
The computer that has Qt4 recognizes all 14 file formats as image files.
So, what's your professional verdict? What do you think could be wrong? Many thanks!